Ends early round syndiebombing

Restricts the beacon items (singulo beacon and syndicate bomb) from the first 40 minutes of play in traitor. Nuke Agents can still use these items at will, but for normal traitors they will be stuck holding the beacon in the meantime. The descriptions of the items in the uplink have been altered to reflect this caveat.

Between this and #4681 hopefully #4673 won't be needed anymore