Move to the new texture system, bug fixes and lens bench GUI.

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.
Client classes moved to client package.
Added @Override tags, for faster updates in case of changes in method naming.
Added slots and inventory classes.

Known issues:
Some textures are missing and are still registered, like some colored ones.
Blocks have invalid or non-existent names in custom tab.
Slots aren't finished and could cause crash when used.