Removed unused lava texture

Removed unused (and illegal) lava_flow.png
Added Waterstone

Added:
New class for Waterstone, so particle effects may be implemented later.
Code to add Waterstone.
Crafting recipe for Waterstone.
Modified lavastone textures for Waterstone and any other fluid blocks in
the future.
English language entry for Waterstone.
Merge pull request #2 from Solestis/add-waterstone

Add waterstone block