This fixes an issue where the existing PreferencesFragment was discarded when
restoring PreferencesActivity from instance state. This issue caused the
PreferencesFragment to no longer receive activity results. Most notably, this
resulted in 0 byte vault files being created when exporting the vault.
added two new theme options:
SYSTEM: dynamically switches between light and dark
SYSTEM_AMOLED: dynamically switches between light and amoled
reversed workaround for amoled themed preferences
launch screen now always follows the system theme