add a couple more spotter options - start after x laps, start after x sectors

[mrbelowski]

start_after_laps would allow you to have the spotter switched off for lap one - good for manually controlled rolling starts

start_after_end_of_sector - can be used to start the spotter after we finish sector 1 (or whatever) - could be combined with start_after_laps. This wouldn't work well in raceroom as it doesn't have reliable sector tracking