Remove usage of menus/menus.txt

Position/alignment is now in the config files for each individual menu.
Add toPoint() and toRect() to file parsing utility functions
Use utility functions to simplify parsing menu config files
Allow position configuration for MenuNPCActions

Fixes #996
Rename some instances of update() in menus to alignElements()

update() implies that the function can be called multiple times (usually
every frame). In contrast, alignElements() is typically called just once
after a call to align().