Sharing system, FPV soldier, co-commander, team chat, pings and voice chat - #507

Stacked PRs, merge in this order: #508 → #509 → #507 → #511 → #510
Until the ones before it are merged, this diff also includes them.

Only this PR's changes: changes since #509

• Alliances, allied control and sending resources go through one sharing system
• Soldier: an FPV player joins a commander's team, shares their vision, gets a fixed kit, follows orders and respawns at their buildings, with their own HUD
• Co-commander: two players on one capitol, like Archon mode
• Team and all chat (! for all chat, spectators only talk to spectators), gamerule to turn all chat off
• Ping wheel on the minimap, in the world and in team chat, with pixel symbols
• Optional Simple Voice Chat bridge: local, squad, team and all channels per role; the voice channel follows the chat channel and shows in the chat panel, team voice includes allied soldiers
• Soldier and co-commander options in match setup: players ask to join in the roster and the seat holder accepts or refuses. Enemy picks can't be hidden while these are on

Roles are optional and off by default. Not tested a lot yet.

• In RTS view, units hidden behind blocks show as a see-through silhouette in their owner's colour, and underlines show through blocks but stay under unit models