No back icon in action bar of APN Settings

When entering the APN menu, the actionbar is missing a back
icon allowing the user to go back to the previous pane.

Added parentActivityName in ApnSettings, to enable action
bar back icon.

Change-Id: Iee8bb420f47c0e2c0d9a43739f534466abba30db
Merge "No back icon in action bar of APN Settings" into cm-10.1