Move rake initialization into CLI

This avoids double-call scenarios of PadrinoTasks.init that lead
to fake warnings and double-loading of tasks.

Fixes #1109
Refactored the admin generators to support namespaced apps and to read a
bit better. Also disabled `-a` since it wasn't really doing anything and
left a few notes to implement them. Please, see the conversation at:
https://github.com/padrino/padrino-framework/issues/854#issuecomment-14749356
I don't think this should be a blocker to release 0.11.0 and the rest of
the admin needs to get there in time!..

I also added some tests and refactored existing ones so they make sense.
A few need to be implemented though. Tests are now (almost) in mini test format - moving them slowly away from shoulda/mocka.
Merge remote-tracking branch 'upstream/master' into super-admin
Merge branch 'super-admin' of github.com:WaYdotNET/padrino-framework into super-admin