UI: Use new style for milestone detail page

Depends on !1953

See the commits for more details, the messages mostly speak for themselves.

Before:

![Screen_Shot_2015-12-02_at_17.47.03](/uploads/62441f50963e0c5d6d04b065573c05f0/Screen_Shot_2015-12-02_at_17.47.03.png)

After:

![Screen_Shot_2015-12-02_at_17.47.22](/uploads/ab29ac0c1819415cc647be173f8c92bd/Screen_Shot_2015-12-02_at_17.47.22.png)


See merge request !1966