Show main supply count in scoreboard

[LordDz]

Adds "Supplies: " to the scoreboard, to make it easier for both the team and ASL to see how much supplies is left for the team to use from the main supply.

Just another small commit to make the game easier to play and less of a guesswork on how much supply a logistic truck will spawn with spawn, while the team can also see if the logistic players can still afford to construct buildings.

Similar to https://github.com/DarklightGames/DarkestHour/pull/1673