Use patch for email-like quoting with '>' chars.

Apply the patch from https://github.com/Bitmessage/PyBitmessage/pull/271
for email-like "reply below text" with '>' quoting.  The patch is
slightly modified compared to the referenced pull request.
Make reply below quote opt-in.

Add a new preference for 'reply below quote' and only use the new
quoting style if it is set.
Merge branch 'master' into email-quoting
Merge pull request #633 from domob1812/email-quoting

Optionally reply below quote (email style)