When a GAction is activated by a menu, or by a toolbar button, you can
now use GAction::activator() to get a pointer to whomever activated it.
This can be used to implement context-specific behaviors in situations
where the same action is exposed through multiple paths.
This addresses an issue that was brought up in #826.
This changes the behavior of the "is_checkable" flag on GAbstractButton
to only be about user interaction checkability. In other words, it now
only prevents the user from checking/unchecking the button, the code.
Instead of LibGUI and WindowServer building their own copies of the drawing
and graphics code, let's it in a separate LibDraw library.
This avoids building the code twice, and will encourage better separation
of concerns. :^)
