feat: Multiplayer (#2)

Make this game multiplayer.

Setup:
- `common` for common classes used both by the server and the client
- `game` the actual client
- `server` the server

Reviewed-on: https://gitea.local.jzitnik.dev/jzitnik/game/pulls/2
Co-authored-by: jzitnik-dev <email@jzitnik.dev>
Co-committed-by: jzitnik-dev <email@jzitnik.dev>

common/.idea/.gitignore

@@ -0,0 +1,3 @@
+# Default ignored files
+/shelf/
+/workspace.xml