Add HTML5 input support

Adds support for html5 `color`, `datetime`, `datetime-local`, `week` and `search` input types to `CHtml` and `CActiveForm`.

I think we should also consider making `CHtml::activeInputField()` public rather than protected, it would make it easier to support custom input types if the framework doesn't support them.

Todo:

- [x] Update changelog
- [x] Add these fields to form builder