Update/Add links under Help/About menu (#1377)

Initiated by user feedback, this PR updates some links under the "Help" menu, now renamed to "About". Summary of changes:

Remove the How To / Tutorials link. This just pointed to the community site under a sub-category called How To / Tutorials. It's not well maintained.
Removed the tour link (we no longer pay for HelpHero - it never worked very well)
Add a link to YouTube videos
Add a link to Known issues and limitations on GH wiki
Rename "What's new in the app" to "What's New" and link to the post that @alex-larkin maintains for release summaries
re ordered the links a bit
added font awesome v4 icons

src/Site/views/languageforge/container/languageforge.html.twig

@@ -16,15 +16,13 @@
                 </span>
                 <ul class="nav navbar-nav">
                     <li class="nav-item" uib-dropdown>
-                        <a class="nav-link" uib-dropdown-toggle href id="helpDropdown" aria-haspopup="true" aria-expanded="false"><i class="fa fa-life-ring"></i> <span>Help</span></a>
+                        <a class="nav-link" uib-dropdown-toggle href id="helpDropdown" aria-haspopup="true" aria-expanded="false"><i class="fa fa-question-circle"></i> <span>About</span></a>
                         <div class="dropdown-menu dropdown-menu-right" uib-dropdown-menu aria-labelledby="helpDropdown">
-                            {% if projectId is not empty %}
-                                <a class="dropdown-item" target="_blank" href="https://hlp.sh/t/_/GsubLqNFYR2?~id={{projectId}}">Start Language Forge Tour</a>
-                            {% endif %}
-                            <a class="dropdown-item" target="_blank" href="https://community.software.sil.org/c/language-forge/how-to">Tutorials and How-Tos</a>
-                            <a class="dropdown-item" target="_blank" href="https://community.software.sil.org/c/language-forge">Community Support</a>
-                            <a class="dropdown-item" target="_blank" href="mailto:[email protected]">Report a Problem<br />(email [email protected])</a>
-                            <a class="dropdown-item" target="_blank" href="https://github.com/sillsdev/web-languageforge/releases">What's new in the app?</a>
+                            <a class="dropdown-item" target="_blank" href="https://community.software.sil.org/t/w/5454"><i class="fa fa-gift"></i> What's New?</a>
+                            <a class="dropdown-item" target="_blank" href="https://www.youtube.com/playlist?list=PLJLUPwIFOI8d8lmQVAcBapyw87jCtmDNA"><i class="fa fa-youtube-play"></i> Videos</a>
+                            <a class="dropdown-item" target="_blank" href="https://community.software.sil.org/c/language-forge"><i class="fa fa-users"></i> Community Support</a>
+                            <a class="dropdown-item" target="_blank" href="https://github.com/sillsdev/web-languageforge/wiki/Known-Issues-and-Limitations"><i class="fa fa-exclamation-triangle"></i> Known Issues and Limitations</a>
+                            <a class="dropdown-item" target="_blank" href="mailto:[email protected]"><i class="fa fa-envelope"></i> Report a Problem<br />(email [email protected])</a>
                         </div>
                     </li>
                     <li class="nav-item dropdown" uib-dropdown>