If app goes to background while on image picker or action sheet, remove
those screens if app enters background:

Why?
- Apple recommends that apps that show an alert view or action sheet remove these from the screen when the user presses the Home button to put the app in the background. The user may return to the app hours or days later and they’ll have forgotten what they were going to do. The presence of the alert view or action sheet is confusing and users will be thinking, “What's that thing doing here?!”