Implementing mobile:background command for Android and Selendroid
Remove debug log
Tidy up spaces according to pull request review
Fixed indentation according to Appium project style guide (2 spaces indent)
Fixed error management in background method
Add an argument to ADB.startApp in order to choose whether to stop the app prior to starting it
Refactored mobile:background method for Android: using ADB.startApp rather than directly issuing am start command to ADB shell, do not return to callback until app is back to foreground
Mimick the launcher start intent for the app when starting it

The Android launcher uses the following settings to start apps:
- MAIN action
- LAUNCHER category
- FLAG_ACTIVITY_NEW_TASK
- FLAG_ACTIVITY_RESET_TASK_IF_NEEDED
Without those settings there were discrepancies between Selendroid and
Android when trying to bring the app back to foreground: it would not
bring back the existing Activity stack but create new activities
Merge branch 'background-android'

Conflicts:
	lib/devices/android/android-common.js