Fixes#342
- using regex pattern/matcher to escape chars below 0x0020 and
above 0xd7ff
- using String.Replace to escape XML entities
- changed XmlPullParser from Xml.newPullParser() to
XmlPullParserFactory parser to fix import on GB
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.