Update doc header/footer
Update the documentation header and footer to be consistent with the MIT
App Inventor website.
<a class="dropdown-item" href="http://appinventor.mit.edu/explore/app-month-gallery">App of the Month</a>
<a class="dropdown-item"
href="http://appinventor.mit.edu/ai2/ReleaseNotes">Release Notes</a>
+ <a class="dropdown-item" href="http://appinventor.mit.edu/about/termsofservice" target="_blank">Terms of Service</a>
</div>
</li>
<li class="nav-item dropdown">
target="_blank">Open Source Information</a>
<a class="dropdown-item" href="http://appinventor.mit.edu/explore/research">Research</a>
<a class="dropdown-item" href="http://appinventor.mit.edu/explore/hour-of-code">Hour of Code</a>
+ <a class="dropdown-item" href="http://appinventor.mit.edu/explore/resources">Additional Resources</a>
</div>
</li>
<li class="nav-item dropdown">
