Fix TimePickerPreference

[smichel17]

Need to ensure:

• [x] String is stored in SharedPreferences in 24h format (I believe this is currently true)
• [x] Displayed in 24h or 12h format according to system preference
• [x] Time Picker should display according to system preference
• [x] Time picker should open with default values filled according to current preference values.
• [x] [Maybe] Implement as a TimePickerDialogFragment so it can survive rotation.

[smichel17]

Fixed by 771a527