Update AlarmManager Global Settings String

Implements methods that update the AlarmManager Global Settings String
when the user confirms a value in the Dialog. updateAlarmManagerValue
takes the key of the factor being edited and the edited value enterd by
the user in the dialog assigning it as the current value of the key.
This a new string is then rebuilt with the updated values and assigned
to be the new Settings Global String.

Bug: 195056102
Bug: 195055895

Test: Manual
Change-Id: I5776822c665bdfa052f23099d367ba8cf29743df