Fixed several window module api issues

[israel-dryer]

• fixed issues caused by 'falsey' checks on Window and Toplevel parameters
• fixed alpha on Linux
• set platform checks on several platform specific parameters
• updated logic for centering screen, prev method caused issues on Linux when setting alpha; this still does not account for titlebar height however
• replaced height and width parameters with size parameter on Toplevel to be consistent with Window class. The old parameters are still accepted via kwargs. The original arguments were not getting passed to the superclass anyway, so this fixes a bug as well