GRAPHICS: Added changes and improved code from inisider/scummvm (partial text)

Includes code from https://github.com/inisider/scummvm/ , which has been
squashed and bugfixed
GRAPHICS: Add support for Soft Shadows with rounded squares
GRAPHICS: Shadows on tabs
GRAPHICS: Gradient blending on borders of rounded squares
GRAPHICS: Readded (modified)checks for character-drawing
GRAPHICS: Safer memcpy when copying from backSurface to activeSurface
GUI: Text in search-box no longer cutoff