fix power-vacuum determination and adjust errormsg

We should only complain if the user that is to be
deleted is actually an admin herself.
Also the error message should probably be a bit
more informative.
refactor minimal admin count to a constant.
add two spec tests for PowerVacuum error.
Merge pull request #851 from ontohub/849-fix_account_canceling

849 fix account canceling
Merge pull request #850 from ontohub/367-add_box_shadow_to_search_bar

367 add box shadow to search bar
Merge branch 'staging' into 825-hide_other_dropdown_menus

Conflicts:
	public/static/gwt/ontohub.nocache.js
Merge branch '825-hide_other_dropdown_menus' into develop

Conflicts:
	public/static/gwt/ontohub.nocache.js
Merge branch 'develop' of github.com:ontohub/ontohub into develop