Make use of modern-style quotes

Make use of modern-style quotes

(See issue https://github.com/DTVD/rainbowstream/issues/134)

Twitter introduced a new way of quoting, by simply putting the tweet url
as a quote. The web interface (and most clients) will then display a
preview of the quoted tweet, leaving more characters available for your
quote.

This patch change the default quote format from the old mode ("#comment
RT #owner #text") to the new one, introducing a new #tid keyword holding
the tweet id (needed to find the tweet URL). It's still possible to go
back to the old mode, by changing the QUOTE_FORMAT config parameter
back to "#comment RT @#owner #text".