Add ol.dom.Input

Allows to bind an HTML input to an `ol.Object` (and vice versa).

The input type can be `text`, `number`, `range` (for string or number), `checkbox` or `radio` (for boolean values).

Depends on #370 (wrong missing goog.requires)

Rotation slider:
http://dev.camptocamp.com/files/fredj/dom-object/examples/rotation.html

Visibility checkbox, opacity slider:
http://dev.camptocamp.com/files/fredj/dom-object/examples/semi-transparent-layer.html