Basic, single-team gameplay

reviewer: @desirino 

Changes:
* Add runner camera positioning.
** Camera is aimed at 1/3 of the viewport width ahead of user-controlled runner.
** Except when the lead runner in the team is so far ahead that they'd be nearly off-screen. in this case, the camera is offset to ensure the leader is always visible.
** If the user-controlled runner goes out of view due to the above, the player is killed.
* Add level segment removal.
* Change level segment addition and removal to consider the position of all team-members.
* Add observer view, camera is centered on the average position of all team-members.
* Add commander player
** Commander camera and game object move with the runner's average position
** Commander will move to the position of the user's touch/mouse
* Change in-game debug ui to display more relevant information based on game state.
* Add end-game condition checks
** End game if all teams are dead (no active runners in any teams).
** Track team distance.
** Basic handling of player disconnection handling and team validity checks.