Add support for verifymessage and sendrawtransaction

This pull request depends on the features in https://github.com/bitpay/insight-api/pull/233.

This pull request implements the front-end for the `/api/messages/verify` (Bitcoin RPC verifymessage) and `/api/tx/send` (Bitcoin RPC sendrawtransaction) API features. The corresponding front-end routes are, unsurprisingly, `/messages/verify` and `/tx/send`. Links to the new views are added to the footer, next to the language selection.

The features can be tested at http://koirikivi.fi:3001/. Note that the server runs against testnet, with both historic and p2p sync disabled (hence the warning on the index page), because of the limited hardware on the server.