Cache: Use Cache Group instead of 'prefix'
Cache: Simplify cache names
Cache: Utilize Cakephp's Cache Group feature

This simplifies cache management and especially clearing the cache
in CachedBehavior. Instead of looping through an array of registered
prefix, just call clearGroup().
Cache: Add missing DS
Cache: Rename config to 'cached_settings'
Croogo: Cache event handlers
Acl: Update cache config/group name
Merge branch '1.5-cache-groups' into 1.5
Fix: SocketException from CakeEmail causing SecurityError

Closes #375
CroogoPlugin: Check for empty argument
CroogoPlugin: Use unlink for symlinks
CroogoTheme: Extract method CroogoTheme::delete()
Merge branch '1.5-extensions' into 1.5

- Safe when deleting symlinks of plugin/themes (original is not touched)
- Extract method CroogoTheme::delete()
- First Push from new house :)
Install: Disable Cached behavior during install

Closes #380
CakeEmail::theme() acts as a getter with an empty value

This causes "Fatal error: Call to a member function viewVars() on a
non-object" is some cases.

Closes #381
UsersController: Improve method _sendEmail()

- Reusable across the controller
- Fix error when sending email forgot password.
Cache: Change back to use prefix

The following caching scenario is broken due to 5377f55c754:

Blocks with visibility path set is not cached correctly. This is due to
codepaths that generate different cache files is not entered in CroogoAppModel
since 'prefix' is not set.
Contacts: Use appropriate value for menu name
Fix: Block 'shortcode's are not filtered

Closes GH #166, GH #109