QRentBook: LSK and RSK of booking page will change somethimes

Steps:
1. Start Qrentbook application
2. Select option-> manage resources to add two new resources
3. Back to startup screen
4. Select one book resource, book it
5. Select "option"->"Manage resources"
6. Select "Back" to application start up screen
7. Select the booked resource, tap "delete", then cancel it
8. Repeat step 7 for several times

Expected Result: In default, the Left software key is "Cancel", the Right software key is "Ok"

Actual: The Left and Right software key will change to different symbol
More details please refer:https://qtrequirements.troll.no/browse/QTTH-1442