Upgraded UI Bootstrap to 0.7.0, Angular to 1.2.3.

* Re-implemented the dialog service since it was removed in 0.6.0.

Angular UI 0.5.0 fixed a major performance problem with the collapse
directive[1] that was polling the scrollHeight of its element and
forcing unnecessary layouts.

[1] https://github.com/angular-ui/bootstrap/commit/a72c635c7669933204c17bf85cfe3d4fc350c73a

Review: http://reviews.apache.org/r/16264