TriggerMenu: Further python3 fixes

• Fix relative imports.
• iteritems
• can't use -1 for level in import
• use zip instead of map with a null function
• print function.
• generators -> list
• builtin -> builtins
• comparison/sort incompatibilities
• integer/float division
• metaclass fix
• exec statement

(Still have to fix uses of exec to set local variables. Will be addressed in a subsequent merge, to keep this one from getting too big.)