Change some events, fix p2 sending gameend twice

- Fixed gameend being sent twice in p2
- Add `ready`, `loader-error`, and `song-select-random` events
- Fixed `session-start` not firing when invited, added event detail
- Fixed `language-change` being fired at startup
- Fixed `version-link` and `about-link` firing twice
- "#song=" will fire `song-select-difficulty`
- Removed `key-events` and `scoresheet-player2`, merged with `scoresheet` and made it more detailed

server.py

@@ -210,6 +210,7 @@ async def connection(ws, path):
 								user["other_user"]["ws"].send(sent_msg1),
 								user["other_user"]["ws"].send(sent_msg2)
 							])
+							del user["other_user"]["other_user"]
 							del user["other_user"]
 					else:
 						# Other user disconnected
@@ -304,6 +305,7 @@ async def connection(ws, path):
 								user["other_user"]["ws"].send(sent_msg1),
 								user["other_user"]["ws"].send(sent_msg2)
 							])
+							del user["other_user"]["other_user"]
 							del user["other_user"]
 					else:
 						# Other user disconnected
@@ -324,6 +326,7 @@ async def connection(ws, path):
 				user["other_user"]["ws"].send(msgobj("gameend")),
 				user["other_user"]["ws"].send(status_event())
 			])
+			del user["other_user"]["other_user"]
 		if user["action"] == "waiting":
 			del server_status["waiting"][user["gameid"]]
 			await notify_status()