Sign in redirection

Changed redirection destiny after login mechanism.
The destiny is resolved this way:
- use scrooge-home if installed and user has perm. to it, else
- use assets-home if installed and user has perm. to it, else
- use core-home if installed and user has perm. to it, else
- 403.

Added factories:
- GroupFactory
- BoundPermFactory
- UserFactory

@quamilek @ar4s 
Url with ``home`` name is defined somewhere in Ralph?