Fix / improve custom gametype handling

• Fix custom gametype name not correctly displayed as scoreboard title and as gametype winner in the map vote
• Fix current custom gametype not being kept if gametype vote ends without votes
• Make sure active custom gametype is not kept on the next map after manual gametype command call (and map restart). Currently custom gametypes can only be set after the game is over thus the gametype command doesn't support them

Extra:

• Remove a redundant LOG_TRACE("Selected gametype is not supported by any map");, a similar message is already printed to server console via a bprint