Android: Fix bad copy/paste where volumeDown called volumeUp.

Thanks to Mehmet for reporting the issue.
Add setAirPlayServiceMode() method to discoveryManager for iOS
Fix displaying picker on iPad
Merge branch 'sdk_1.2-dev' into sdk_1.3-dev
Fix setting mode to media. Show alert if AirPlay is not enabled.
Merge commit '3534c267ee2c83a57aeee0d9b13335f2d35380a8' into sdk_1.3-dev
Add instructions for pulling different branches, troubleshooting
Fix passing airPlayServiceMode option to startDiscovery().

Add warning about changing this mode after discovery is started.
Fix crash dispatching commands in objc_msgSend