Subclass action

This moves the Action to be an extension of QtControls Action.  The controls action is not completely aware of the UI state, so we still need a few properties specific to Material.
One concern I have is that the QtQuick Controls Action says that `iconName` pulls from the current system icon theme. Now, Google has released an icon set for Material Design, but it has it's own naming scheme, not the standard Linux naming system. So I have the special Icon class to load the icon based on name, size, and color.

Basically, we need to explain how the `iconName` property works in QML Material, and link to the Google icon set (google.github.io/material-design-icons/).