Fix app not exiting when pressing back key at the top level
Fix app not exiting when pressing back key at the top level

- Pressing the back key would have not effect when at the top level

- This fix rejects the event which lets it propagate to be handled
  by the system

ealloradai/devdays14,ealloradai/devdays14,ndesai/devdays14,ealloradai/devdays14,ndesai/devdays14,ndesai/devdays14,ndesai/devdays14,ealloradai/devdays14