index: Don't drop query parameters when redirecting to dashboard
iframe: Load JavaScript even when 'isIframe' is true
Use lowercase username and user groups for loading user permissions and restrictions
Resources: Support type 'ini' yet only in the resources.ini

Configuring the resource type 'ini' via the web interface is not yet possible.
lib: Add UserGroupBackend as base class and factory for user group backends
lib: Replace Membership with IniUserGroupBackend
lib: Add DbUserGroupBackend
DbConnection::__construct(): Set prefix if configured
Auth: Load user groups using the new user group backends