Move to the new texture system, bug fixes and improvements.

Changed modid to lowcase char, to avoid any possible issue, and to comply with java naming standards.
Blocks first use blockIcon (vanilla variable) for primary texture.
Other textures are only registered once in custom (client-only) variable.
They were moved to a package which allow loading when developping.
Client-only methods are tagged as such to avoid any loading on server side.
Added @Override tags, for faster updates in case of changes in method naming.

Known issue:
Some textures are missing and are registered, like some colored ones.
Blocks have invalid or nonexistent names in custom tab.