Added 2 fixes for when using the installApp, launchApp, removeApp requests seperately

1. Updated the app argument for the installApp, launchApp and closeApp to point to the <b>req.device.arg</b> rather than <b>req.appium.arg</b>. As the app argument was no longer available in req.appium.args.

2. Also added a check for the "installToRealDevice" function to check if "launch" desired capability has not been set to false (as in that instance we want to manage installation and launching ourselves).
Should the same desired capability ("launch") be used for this?