Move the `Add Milestone` button near the top and fix the layout
This commit makes all buttons at the top (roadmap, add milestone and
report) aligned as they should be.
Fixes https://pagure.io/pagure/issue/2860
Fixes https://pagure.io/pagure/pull-request/2895
Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>