1) Allow imports from the stock SMS database at any time.
2) Provide plaintext export support, in a format compatible with
the "SMS Backup And Restore" app.
3) Fix the DB weirdness on encrypted restore that previously
required killing the app.
1) Broke out the UI elements of the major Activites into stylable
attributes.
2) Created a 'light' and 'dark' theme for the newly stylable attrs.
3) Touched up some of the UI spacing.
4) Implemented dynamic theme switching support.
