Point people straight to email for payins/outs

We heard from @jslegers at https://github.com/gittip/www.gittip.com/issues/126#issuecomment-31969020 about the confusing flow for configuring PayPal or requesting bitcoin payins/outs. This PR 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.

@jslegers Is this at all more helpful?