some minor, some major [Take #2]

- state that wiki is an external link (as most external links should)
- add peer4commit as a way to get peercoins
- contribute is now a dropdown menu with the old volunteer form link and
- participate page that should explain how to take part in the peercoin community
- seperate pools to dedicated peercoin pools and multicoins pools that enabels peercoin only mining.
- fix a link from old /r/ppcoin to new /r/peercoin
- add shops that accepts peercoin as payment to resources