Add Builds tab to MR detail page
## Before
![Screen_Shot_2015-12-08_at_13.21.04](/uploads/0d26060bef78f3de076e33439b8a4789/Screen_Shot_2015-12-08_at_13.21.04.png)
## After
![Screen_Shot_2015-12-08_at_13.25.20](/uploads/be7d7fd6d4fc8c5cc366b5b3778b813a/Screen_Shot_2015-12-08_at_13.25.20.png)
Fixes#3907
See merge request !2016