Removed assets/textures/pxm directory

- Relocate *.pxm files to correlating assets directories
- Added line to .gitignore to uninclude .pxm files
Bump build.properties forge_version to 10.12.1.1098
Update build.gradle

- Added function to load build.properties constants as references
- Changed assets directory to run instead of eclipse
- Fixed version & mcversion properties to be injected into mcmod.info
- Excluded .pxm files from .jar build files
Update .gitignore

- Added run directory