Blender Git Loki

Tests: add script_validate_keymap

This checks the generated key-map data matches the result of
re-exporting and re-importing.

This shows up various inconsistencies, including:

- Unused keymaps.
- Unknown/unused data in the keymap.
- Event arguments that don't make sense.
- Event values that don't match the event type
(tweak direction on keyboard event for example).