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).
What do we call 'previous build' ?
I mean: Build X is retried. the previous build is X-1 or X-2 ?

To, me the build previous is always the build with 'number -1'. And If the build is retried, then it seems good to me that the list of changes is empty (no changes was added compared to buildnumber -1).