Create EnterMissionActivity

When Enter Mission button is clicked from MainMenuActivity,
EnterMissionActivity is called.

https://app.asana.com/0/11989140532570/12230414644071
Merge branch 'master' of https://github.com/dhl8282/hobbit
Save full image to hobbit folder

https://app.asana.com/0/11989140532570/12230414644076