Nevanda tileset improvements

[Subc2]

Changes in this version of tileset:

• knight sprite was occupying some of monk's tile pixels
• pyrolisk's wing was cut by several floor pixels
• all vortexes now occupy the same (amount of) pixels and don't have transparency issues
• cleaned up statues of water creatures
• fixed the silver arrow, silver dagger and crystal wand (mostly copied them over from the original JPEG)
• removed some JPEG artifacts