This commit adds the contact name and the readable date (and time) to
the plaintext export of every message. That's because that is how SMS
Backup and Restore does it, so this commit makes Signal more compatible.
Closes#6452
// FREEBIE
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.
