I noticed that the Custom gamemode doesn't appear if the Maps/Custom folder was empty at client start, even if I use /downloadmap and it downloads successfully or I add a map file to the folder using my OS.

Perhaps we should add some kind of file-watcher to the Maps/Custom folder to constantly check if we need to update the Custom maps list and game mode dropdown.

Reproduction:

• Move or delete all files from Maps/Custom
• Start the client
• Start a multiplayer lobby. Custom should not be an available game mode.
• Use /downloadmap HASH to download a map, or add a .map file to Maps/Custom/ using your Operating System.
• Open the game mode drop down again.

Expected: Custom is added to the game mode dropdown after a successful map download or adding a .map file to the Maps/Custom folder. The newly added map is listed as an option in the Custom map list.

Actual: Custom remains hidden even though there are maps in the folder now.