Make the menu button transparent instead of hiding it (Fixes #30)

This way it will still recieves the events, and the (visible) behaviour is unchanged.
Since the button won't react to keyboard, the only way to interact with it is the
mouse and it will appear when the mouse is over it.
Quote arguments in termlets, fixing #165
Merge branch 'issue-30' of https://github.com/abderrahim/finalterm
Update about dialog credits