deathmatch: additional improvements

[jlillis]

This PR makes additional improvements to the new deathmatch resource:

• Fixes a bug I introduced in deathmatch: tiny cleanup #519. Whoops.
• Adds a round start timer
• Disables the area name HUD (dm maps are often made high above the map, area name is not relevant)
• Fixes next round not starting when mapcycler isn't running
• Adds spectator mode
• Adds element data protections

[Nico8340]

So far so good

[Dutchman101]

Is it about ready for review, @jlillis ?

[jlillis]

I had a few other things to add and one last round of clean up in mind. Hoping to have some free time this weekend to wrap up.

[jlillis]

Going to call this ready for review now. Would be nice to see it play-tested with more than myself and a VM to make sure everything works.

[Dutchman101]

I don't see any problems, but due to how niche "deathmatch" is, there is no better way to actually have it playtested than to put it out there. So merging the PR, to be subject to bug reports/addendums by later suggestion.