allow extending of resource list / fix ajax call error

1) allow extending of the resources which on which .need() is called. other packages can import the groups list and easily extend it with other groups or resources.

2) when doing ajax calls, there is often no head. handle this and skip manipulating the head section in this case. maybe the transform should be skipped altogether when doing ajax reqs.

there is still one more bug (or did it work for you once, @garbas): the resources cannot be found. everything registered for ++fanstatic++ is just not accessible. i guess there is another integration layer neccessary.