Add Team chat section (#1067)

* Teamchat: initial commit

* teamchat: remove todo notes from cards

* nav.html: fix teamchat link

* assets: add icons for keybase & rocket.chat

* teamchat: add forum threads

* nav.html: change teamchat icon

* apply Jonah's suggestion on Keybase

* Jonah's & Nitrohorse's suggestions

* update keybase.png

* teamchat: delist mattermost

* teamchat: update description, add links

* update descriptions of apps

* fix keybase description

* teamchat: fix heading

* expand rocket.chat warning

* add missing the

* remove reduntant backslashes

* add teamchat to source_code.md

* small changes

* remove backslashes from link

* teamchat: add Wire Pro as worth mentioning

* remove excess '

_includes/nav.html

@@ -50,6 +50,7 @@
             <a class="dropdown-item" href="/software/encryption-tools/"><i class="fas fa-lock fa-fw"></i> File Encryption</a>
             <a class="dropdown-item" href="/software/file-sharing/"><i class="fas fa-file-export fa-fw"></i> File Sharing</a>
             <a class="dropdown-item" href="/software/im/"><i class="fab fa-telegram-plane fa-fw"></i> Instant Messenger</a>
+            <a class="dropdown-item" href="/software/teamchat/"><i class="fas fa-users fa-fw"></i> Team chat</a>
             <a class="dropdown-item" href="/software/passwords/"><i class="fas fa-user-lock fa-fw"></i> Password Manager</a>
             <a class="dropdown-item" href="/software/productivity/"><i class="fas fa-briefcase fa-fw"></i> Productivity Tools</a>
             <a class="dropdown-item" href="/software/file-sync/"><i class="fas fa-copy fa-fw"></i> Secure File Sync</a>