List all changes related to a build.

 - to do this, the column 'parent_changeid' was added to the table changes

Note:
 - I added a tab 'changes' for the build webpage. I think this should be modified in order to have something more readable (but my angularJS skills are very limited).
That's by far not limited to this commit or this place, but I don't believe ids have anything to do on the web interface. They are just internal data representation details ...