Add Scheduled Start feature
Set 24-hour mode in TimePicker when appropriate
Use preference headers

And move each preference category / header to its own PreferenceFragment
Fix runtime exception in release build

Proguard would rename the settings fragments, so the
`SettingsActivity#isValidFragment()` method would return `false`
Show Action Bar in main activity

With menu containing just “Settings” button
Show correct settings fragment
Fix bug with skipping

Durations for states were reversed