Don't check admin rights on generic_delete

This is the responsability of the caller
Added joe tmp files in ignore list
Added finer permissions

SQL functions to check permissions
wrapper around these in core/perms.py
New system group 9 "observers" that have full read access to everything.
Added permission tests on most groups/event/users
Merge branch 'master' of https://github.com/nirgal/ngw

Conflicts:
	core/models.py