fewer db calls, no sms option on ride creation

[john]

Changes:

• Fewer status changes. They're doing using Rails enum, so a DB call is triggered each time.
• Turn off SMS when bulk uploading rides. We may want to check with ride zone admins about preferred behavior.
• Comments on moving conversion of PotentialRides to Rides to an asynchronous job. That's how it should be done--any upload of more than 200 rides is likely to time out--but I wanted to improve the logic/DB interaction in a discrete step before doing that.