AGS: Implement bits of GUI (buttons, listboxes, editboxes).
AGS: Use the font multiplier for WFN fonts.

This isn't quite an elegant way to do it, but it works for now.
AGS: Fix clipping for mirrored blits.
AGS: Don't add an invalid point to found paths.
AGS: Some more script overlay work.
AGS: Add some area scaling helper functions.
AGS: Fixes/workarounds for some audio issues.