Add support for mapping gestures to scripts anywhere in NVDA.

Currently, there are two global gesture maps: the user map and the locale map.
This allows users and locale maintainers to add new bindings and override existing bindings in a single file.
See the inputCore.GlobalGestureMap class for details.
The user map is stored in gestures.ini in the NVDA configuration directory.
The locale map is stored in locale\LANG\gestures.ini, where LANG is the language code.