Edited request_saved_notification strings.
Added new activity EnterBarcodeActivity.

Edited AddCardActivity to implement EnterBarcodeActivity.
Implemented EnterBarcodeActivity to ReturnBike.
Edited request classes.

Reason: to make data/time field readable.
Added rent bike feature.

Edited RentBikeActivity. Added GetBikeIdActivity.
Edited ReturnBikeActivity.

Implemented GetBikeIdActivity to ReturnBikeActivity.