[theastrogoth]

This fixes the FRLG Sprite Reader, which was my attempt at handling Nidoran genders before the fix that reads the gender characters. It lacked tests and was sometimes unreliable due to how sprites "bounce" when the summary screen is opened.

This does the following:

• adds an option to mirror sprites horizontally in SpriteDatabase (Summary sprites are usually mirrored)
• adds a way to test several windows over the sprite on the screen, shifting a GBA pixel at a time
• adds a sprite reader for battles, which is currently unused but might useful as a fallback for a failed name read or problem with audio detection
• has the sprite reader return a slug with form info to differentiate between Unown forms (possibly helpful for box sorters?)
• reuses test images for the StatsReader and WildEncounterReader

Note to self -- remember to delete the old sprite sheet and duplicate test image after this is merged