Point people straight to email for payins/outs

We heard from a user on #126 about the confusing flow for configuring
PayPal or requesting bitcoin payins/outs. This addresses the issue by
pointing directly to email as the preferred support method for these
requests, rather than linking to the general "Contact us" info.
Merge pull request #1866 from gittip/email-us

Point people straight to email for payins/outs