update mattermost, icecoder, textpad URLs

textpad seems unmaintained since 2016 but
- the program is very simple and does a single task (share public notepads like notepad.cc, simple PHP app)
- someone might want to pick up development and update vendored libraries for compatibility/cleanup/improved security
- no other software in the list seems to fit the same purpose

Ref https://github.com/Kickball/awesome-selfhosted/issues/1013

README.md

@@ -279,7 +279,7 @@ _CalDAV or CardDAV clients._
 - [KChat](https://github.com/php-kchat/kchat) - PHP Based Live Chat Aplication. `Apache-2.0` `PHP`
 - [Lets-Chat](http://sdelements.github.io/lets-chat/) - Self hosted chat suite written in Node. ([Source Code](https://github.com/sdelements/lets-chat)) `MIT` `Nodejs`
 - [Live Helper Chat](http://livehelperchat.com/) - Live Support chat for your website. ([Source Code](https://github.com/LiveHelperChat/livehelperchat)) `Apache-2.0` `PHP`
-- [Mattermost](http://www.mattermost.org/) - Open-source, on-prem Slack-alternative. It can be integrated with [Gitlab](https://about.gitlab.com/). ([Source Code](https://github.com/mattermost/platform)) `AGPL-3.0/Apache` `Go`
+- [Mattermost](http://www.mattermost.org/) - Open-source, on-prem Slack-alternative. It can be integrated with [Gitlab](https://about.gitlab.com/). ([Source Code](https://github.com/mattermost/mattermost-server)) `AGPL-3.0/Apache` `Go`
 - [MiAOU](https://dystroy.org/miaou/login) - Multi-room persistent chat server. ([Source Code](https://github.com/Canop/miaou)) `MIT` `Nodejs`
 - [Mibew](https://mibew.org) - Mibew Messenger is an open-source live support application written in PHP and MySQL. It enables one-on-one chat assistance in real-time directly from your website. ([Demo](https://mibew.org/demo2), [Source Code](https://github.com/Mibew/mibew)) `Apache-2.0` `PHP`
 - [Mumble](http://wiki.mumble.info/wiki/Main_Page) - Low-latency, high quality voice/text chat software. ([Source Code](https://github.com/mumble-voip/mumble), [Clients](https://wiki.mumble.info/wiki/3rd_Party_Applications)) `BSD-3-Clause` `C++`
@@ -1009,7 +1009,7 @@ See https://github.com/n1trux/awesome-sysadmin#monitoring and https://github.com
 - [MiniNote](https://github.com/n1try/mininote) - Simple Markdown note-taking app with persistence. `MIT` `Nodejs`
 - [OpenNote](https://github.com/FoxUSA/OpenNote) - OpenNote was built to be an open web-based alternative to Microsoft OneNote (T) and EverNote. ([Demo](https://foxusa.github.io/OpenNote/OpenNote/#/folder)) `MIT` `HTML5`
 - [Paperwork](http://paperwork.rocks) - OpenSource note-taking and archiving alternative to Evernote, Microsoft OneNote and Google Keep. ([Source Code](https://github.com/twostairs/paperwork)) `MIT` `PHP`
-- [savepad](https://github.com/novavex/textpad) - Minimalist notepad based on notepad.cc. `MIT` `PHP`
+- [savepad](https://github.com/shelltr/textpad) - Minimalist notepad based on notepad.cc. `MIT` `PHP`
 - [ShareLaTex](https://www.sharelatex.com/) - Web-based collaborative LaTeX editor. ([Source Code](https://github.com/sharelatex/sharelatex)) `AGPL-3.0` `Ruby`
 - [Standard Notes](https://standardnotes.org) - Simple and private notes app. Protect your privacy while getting more done. That's Standard Notes. ([Demo](https://app.standardnotes.org/), [Source Code](https://github.com/standardnotes)) `GPL-3.0` `Ruby`
 - [turndown](https://domchristie.github.io/turndown/) - HTML to Markdown converter written in JavaScript. ([Source Code](https://github.com/domchristie/turndown)) `MIT` `Javascript`
@@ -1233,7 +1233,7 @@ See **[Ticketing](#ticketing)**
 - [Babelfish](https://doc.bblf.sh) - Self-hosted server for source code parsing. It can parse any file, in any supported language, extract an Abstract Syntax Tree from it, and convert it to a Universal Abstract Syntax Tree which can enable further analysis and transformation. ([Source Code](https://github.com/bblfsh/bblfshd)) `GPL-3.0` `Go`
 - [Code-Server](https://coder.com/) - Visual Studio Code in the browser, hosted on a remote server. ([Source Code](https://github.com/cdr/code-server)) `MIT` `Nodejs/Docker`
 - [Eclipse Che](http://www.eclipse.org/che/) - Open source workspace server and cloud IDE. ([Source Code](https://github.com/eclipse/che)) `EPL-1.0` `Docker/Java`
-- [ICEcoder](https://icecoder.net/) - ICEcoder is a web IDE / browser based code editor, which allows you to develop websites directly within the web browser. ([Demo](http://demo.icecoder.net/ICEcoder/), [Source Code](https://github.com/mattpass/ICEcoder)) `MIT` `PHP`
+- [ICEcoder](https://icecoder.net/) - ICEcoder is a web IDE / browser based code editor, which allows you to develop websites directly within the web browser. ([Demo](http://demo.icecoder.net/ICEcoder/), [Source Code](https://github.com/icecoder/ICEcoder)) `MIT` `PHP`
 - [JS Bin](http://jsbin.com/) - Open source collaborative web development debugging tool. ([Source Code](https://github.com/jsbin/jsbin)) `MIT` `Nodejs`
 - [Judge0 API](https://api.judge0.com) - Open source API to compile and run source code. ([Source Code](https://github.com/judge0/api)) `GPL-3.0` `Ruby`
 - [Koding](http://www.koding.com/) - The simplest way to manage your entire Dev Infrastructure. ([Source Code](https://github.com/koding/koding)) `Apache-2.0` `Nodejs`