Initial version of the ui-input directive - RFC

This is initial version of the code for the new ui-input family of directives (ui-input, ui-select, ui-textarea) as described in the issue #189.

You can see it in action in this plunk: <http://embed.plnkr.co/TT1t1p>

From the last discussion on the mailing list several things have changed:
* validation messages now can be configured on a module level
* familly and kind of a input's template can be configured on a module level
* select and textarea are supported

There are still plenty of things that should be discussed done (no tests for the moment!) but I feel like this is a good starting point. I've started to use it a bit already and it is extremely powerful, it really makes it possible to write forms with the consistent look & fell - fast!

Let's discuss the concepts behind and the implementation itself!