Add button for removing source branch for merged MR's.
Merge branch 'remove_source_branch_button' of https://github.com/jacob-carlborg/gitlabhq into jacob-carlborg-remove_source_branch_button

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Conflicts:
	app/assets/javascripts/merge_requests.js.coffee
	app/assets/stylesheets/sections/merge_requests.scss
	app/controllers/projects/merge_requests_controller.rb
Merge branch 'jacob-carlborg-remove_source_branch_button'