move themes code into OpenProject's library
fix a wrong css class regarding themes
refactor themes backend
* extract theme finding code from the Theme class into a ThemeFinder module
* omit a trailing 'Theme' in the class name for default identifier and name attributes of themes
* remove the default? method
* do not rely on AS::DescendantsTracker anymore, although it was nice
let's call the default theme 'OpenProject'. alternatively one could have changed the class DefaultTheme to OpenProjectTheme and let that be the default theme.
Fix 'previous' pagination label.
Swap priority of session param and options param.

The options param should have a higher priority. Otherwise the 'page per param' setting
cannot be changed anymore by the user as soon as a session value is present.
Add test.
Remove (hopefully) superfluous TODOs

[ci skip]
Merge pull request #230 from opf/feature/rails3-themes-refactoring

Refactoring of Themes Backend
Add changelog entry.
Merge pull request #241 from opf/feature/rails3-fix-pagination

[OPF#1214] Fix pagination
Add settings for brute force prevention
Block user on too many failed logins within specific period
Add cuke for brute force prevention; also add timecop
Add missing migration for brute force prevention
Add user helper for formatting user status

This thing is a bit ugly.
Add user helper for creating lock/unlock/unblock buttons
User/edit: Add buttons for changing user status incl. unblocking

Conflicts:
	app/controllers/users_controller.rb
	features/step_definitions/user_steps.rb
User index: show status and allow filtering by status
User index: show blocked and locked users under "permenently locked"