Module API refactoring

[Robin Böning]

Thanks Thomas for refactoring the whole module API that allows us to
plug in new modules very very easy now!

(Actually therese changes has been made in the next_stable branch)

[Thomas von Deyen]

My pleasure. ^_^

Next I'm planing to add helpers and sass-mixins to make Alchemy a first class rails admin backend.
So the module development will get even easier.

So I want to introduce an alchemy module resources controller, that a plugin could inherit from.
So all resourceful methods would already be there.

Also I want to introduce some admin view helpers for the toolbar and the table views.

@robin: you played around with fancy-grid, aren't you? Maybe we could use this, for sorting and filtering?

Any more ideas?