More client code quality improvements, removing more unused assets

[StenAL]

This PR contains a bunch of cleanup but no functional changes:

• NOP is renamed to number of players, without deep context it is not obvious what the (R)NOP classes were doing
• Static initializer blocks were removed in favor of initializing static fields in their declarations
• A bunch of unused assets were removed, mostly related to AGolf2 but also some old server code relics and assets from other games
• A bunch of small code quality improvements:
  • Use integers instead of chars in math operations
  • Use more magic constants where possible
  • Remove more unused imports
  • Remove useless JavaDocs that just say "Playforia"
  • Remove some explicit uses of UTF-8 enconding. This is the default encoding since Java 18.
  • Remove unused LobbyRef class