Fix turtle speaker upgrade's missing texture #508
There's two parts to this commit: a simple fix, and a more comprehensive fix. Feel free to cherry pick one as desired.
The simple fix (2e7302e) simply adds the speaker texture to the texture sprite. As of MinecraftForge/MinecraftForge@7892ca9 the texture will not be automatically detected as resources are only loaded once.
The more comprehensive fix (80b1170) will automatically extract textures from the upgrade models. This has the advantages that we don't need to register textures ourselves, and also allows resource pack makers to use different texture names for upgrades.