Make actionbar change more visible in changelog

By adding a visually separate and bold section and having a link to our FAQ where the change is explained in more details.
Note: The link wont work, as this section of the FAQ is currently set offline but will be put online before releasing.
Test HTML heading tag in changelog

According to http://commonsware.com/blog/Android/2010/05/26/html-tags-supported-by-textview.html it should be supported even in textview.
Clean up old changes

- Clean up changes from older releases
- Add link to milestone
Merge pull request #4113 from cgeo/release

Merge release to master