big work
what was reliable before is now not, in recent versions of renpy, which is why we added that new config (which I put in say.rpy, but it can be moved somewhere else)
Also fixes the game_menu's title position, incidentally
some changes are incompatible with my diary and achievement branches, respectively, they will need to be merged with a bit of manual care
- don't use a reserved name (starting with an underscore)
- use a file-local mangled name (starting with two underscores
- use renpy.dynamx to cleanup the variable automatically
(cherry picked from commit 3e86094b0b)
