Variable Padding for TextWindow GUIs

Removed the hardcodedness of padding around text windows in a
*hopefully* backwards compatible way. Made use of popupyp, which was
previously unused for TextWindow GUIs.
Padding Fixes

Made padding a little less resolution dependent and fixed a whoopsie.
More Padding Fixes

Notices a few more whoopsies when comparing code.
Engine: Better portrait character X positioning

The engine will now check to see whether the portrait needs to be on the
left or right when in "Sierra-style portrait location:
BasedOnCharacterPosition" mode even if the character speaking is the
same. This fixes situations where a player might speak to a character,
then move around to the opposite side of that character and speak to
that character again.
Merge branch 'portrait_location' of https://github.com/gurok/ags into portrait_location