Further improvements of admin interfaces

* Change how receivers and contexts are picked to not use select2
  fixes: https://github.com/globaleaks/GlobaLeaks/issues/68
  and closes #31
* Move the field editor into a separate template
* General improvements to look and feel of app
Move delete and add buttons to the top
Merge remote-tracking branch 'origin/master'

* origin/master:
  Remove dead code.

Conflicts:
	app/views/admin/contexts.html