Vessels: Smaller/improved textures, remove duplicated 'inv' textures

Removed unnecessary inventory textures
The drinking glass inventory texture now differs from
the node texture to be more clearly a drinking glass
Smaller textures to reduce size as nodes

mods/vessels/README.txt

@@ -43,3 +43,8 @@ Authors of media files
 Unless specifically noted,
 Copyright (C) 2012 Vanessa Ezekowitz
 
+The following textures were modified by Thomas-S (License is CC0):
+    vessels_drinking_glass.png
+    vessels_drinking_glass_inv.png (Paramat helped to improve this texture)
+    vessels_glass_bottle.png
+    vessels_steel_bottle.png