Undoview adjustable height

I have added 2 features:

1. Modified the "inflate" method for the "undo" layout, now a parent is provided otherwise the layout_* parameters of the "undo" view are ignored (It's impossible to set a fixed height to the undo view directly from the xml)

2. Added a new api setKeepHeight(boolean) to the ContextualUndoAdapter: with this is possible to set the height of the undo view as the height of the content view. The default is "false"

Thanks,
Giuseppe