Add Motorcycle/dirt bike activity types

[KevinUptain]

I know that Strava doesn't want to support motorsports, but people want to track their dirt bike rides, and so they are using E-bike activities to do that. Where I live there are a lot of mixed use trails, so people on their dirt bikes are messing up the segments for actual E-bike activities. Just add an activity for motorcycles, easy solution. I don't currently ride a dirt bike, but if I did, I would want to track it too. 

[Bryant]

Hey @KevinUptain,

You are correct we don't want to encourage motorsports but you do make a compelling argument about those who record motorsport activities and upload them as ebike anyways.

It has been reviewed by our moderation team and is now open to voting.