Creates an activity to manage the settings of any document provider
that needs them, and populated it with the settings required by the
ownCloud implementation.

The settings screen is not yet plugged to the document browser UI but
can be launched with this command:

  adb shell am start -a android.intent.action.MAIN \
  -n org.libreoffice/.storage.DocumentProviderSettingsActivity

Change-Id: I83cff641fa61078f2bddbb98262af989c06985a9
Reviewed-on: https://gerrit.libreoffice.org/16193Reviewed-by: Jacobo Aragunde Pérez <jaragunde@igalia.com>
Tested-by: Jacobo Aragunde Pérez <jaragunde@igalia.com>