We use the PreferenceFragment framework provided by Android to
display settings and allow the user to modify them. The API doesn't
support dynamic preference changes from a non-user source, such as
loading the preferences from a file.

Previously, after importing the settings from a file the user would go
back to the PreferenceActivity and would see the old (pre-import)
values, even though the saved settings had been correctly loaded.

This commit provides a stop-gap solution to the issue by
finishing the PreferenceActivity when the user imports settings, the
rationale being that forcing the user to re-navigate to the settings,
while slightly annoying, is much better than making them think we hosed
their data.