Bug 834542 - [LockScreen] Display time in the statusbar for the Emergency Call screen. r=timdream

Add event listeners for lockscreen events in the StatusBar in order to correctly
display the statusbar clock according to the lockscreen panel:
- main: hide clock
- passcode: hide clock
- emergency-call: show clock
Merge pull request #9218 from mcirlanaru/bug_834542

Bug 834542 - Display time in the status bar for the emergency call screen, r=@timdream