Fix validaiton of --clean

Check !== FALSE since passing --clean just sets it to NULL
Make sure we handle duplicate users properly
Import: Delete users with NULL username when passing --clean
Add @todo to handle existing categories during import
All mixed up

For some reason I got mixed up and changes reverted, so this commit has some of yesterday's general UI fixes ...

as well as questions on why adding the "create set" modal is so darn difficult. Also, my sets view has disappeared from #sets href
Merge branch 'master' into create-set-modal

Conflicts:
	modules/UshahidiUI/media/css/global.css
Remove sass-cache again
Fix create set modal

Fix the JS error in SetsView: events shouldn't be inside 'initialize',
and you need to add the showCreateSet handler function
Rename the event to 'set:create'
Merge pull request #105 from ushahidi/create-set-modal
Upgrade backbone to fix issues with models getting the wrong URL

This bug https://github.com/jashkenas/backbone/issues/2416 means that
models
fetch by a collection get their url set to the collection url, not
individual model urls.
Upgrading backbone to latest master to fix, waiting for next BB release.
Merge pull request #103 from ushahidi/migration-script-fixes

Migration script fixes
Make sure import tests reset the DB before they run

Make the TaskImport2xTest extend DB testcase and add the usual dataset
Removed repeated instructions
Merge pull request #112 from ushahidi/readme

Removed repeated instructions
Load google fonts over http/https as needed

Use // urls instead of http:// or https:// for loading google fonts
Merge branch 'master' into create-post

Conflicts:
	modules/UshahidiUI/media/css/test/global.css
	modules/UshahidiUI/media/js/app/controllers/ModalController.js
	modules/UshahidiUI/media/js/app/templates/modals/CreatePost.html