Some usability fixes for members selection with select2:

* Roles will not be loaded remotely anymore
* Users will now load immediately and do not require user input
* The select boxes are now right next to each other

Conflicts:
	app/assets/javascripts/members_select_boxes.js
move the placeholder of members selection boxes to associated labels

Conflicts:
	config/locales/en.yml
member select box labels are no longer bold
fixes tabbing issue with roles search box
Added changelog entry
Merge pull request #235 from opf/fix/select2-members-usability

Some usability fixes for members selection with select2: