Add PopupMessage module.
Import PopupMessage in WindowManager.
Add code to display PopupMessage.
Add temporary start menu entry for testing.
Fix missing arguments.

This is the first working commit for showing popup messages.
Better align popup message text.
Blur the background behind the popup message.
Draw a box around popup message text.
Add a PNG for the gradient for the background of popup messages.
Darken the popup background with a gradient instead of a solid color.
Merge remote-tracking branch 'origin/popupmessages'