Added Checks for Existence of Key

https://github.com/Asahra/Racetrack/issues/8
Conditional checks added in to check for the existence of the race track
key. If it doesn't exist, then it will show an error. Along with this
change I've added identifiable names to each prefab name field so they
show up in error debug.

http://forums.cloudparty.com/discussion/1903/getparam
Posted a question in relation to getParam() not returning consistent
values to check against. This is in relation to the Racetrack Key
customizer setting.