Icon control

[promag]

Button control is used to show icons because it has support to colorize the image. Button is packed with more stuff like states, event handling, label... eventually a light component should be used instead. For now, abstract the usage of Button in the new Icon control and use it in trivial places. There are more places where Icon can be used but require more changes, so I'm leaving them for follow-ups.

[promag]

Forgot to mention that this is a small step in fixing focus navigation since the previous Button instances had by default enabled: true and so were in the focus chain.