Fix headers of milestone and snippet show pages

Fix layout, and move "Edit" button to very right just like issue/MR.

Before:

![Screen_Shot_2015-12-15_at_17.33.20](/uploads/dbbeb6868b80e21894159126a0feca6a/Screen_Shot_2015-12-15_at_17.33.20.png)

![Screen_Shot_2015-12-15_at_17.33.28](/uploads/53d10b42adc34e48b063889120e9a746/Screen_Shot_2015-12-15_at_17.33.28.png)

After:

![Screen_Shot_2015-12-15_at_17.34.25](/uploads/b0d0ea3f6a7b61d51b474419207f7a02/Screen_Shot_2015-12-15_at_17.34.25.png)

![Screen_Shot_2015-12-15_at_17.35.55](/uploads/65b922f5249655d3733740690577c9d7/Screen_Shot_2015-12-15_at_17.35.55.png)

cc @skyruler 

cc @rspeicher 8.3 please!

See merge request !2104