Change respawns to use frame counts

[za419]

I just realized that rdtsc is probably inappropriate because of the fact that it continues incrementing while the game is paused, so objects can and will tick down their respawn during pause.

Switching to framecounts (as updated in GamePlay), may have some or all of the following benefits:

• Reducing the total size of GameObject tags
  • rdtsc requires 64 tag bits, as 32 bits can only track up to about 4 seconds and 16 is basically instant
  • For framecounts, 16 bits at my guess at our framerate (a fully peasant 15FPS) allows a respawn time of about an hour, 13 minutes, which is a lot more than enough
• Improving the cross-platform consistency of respawn times
  • I don't really know what determines framerate, but it's probably more consistent across machines than the processor's clock speed
• Making respawn times more intuitive to work with
  • Clock cycles are hard to do math around and get into code
  • Frame counts aren't.
• More consistent behavior when game is sharing CPU time
• Fixing #1

[za419]

Using gamescore is a good substitute here, because it is largely a frame counter, and automatically shortens respawns when the player is doing good.