Merge branch 'devs/felipealmeida/emodel'

Efl.Model is an attempt to provide a data model as in the M of MVC to efl core.
A first implementation and example is provided as a Eio.Model. This together with
some patch in Elementary should provide a fully asynchronous and fast modern MVC
system for EFL.

The API has been in review since last summer, but will still only be accessible
with EFL BETA API and EO for now. More data model should come in the future.