Address properties

Endpoint at `/addr/[:addr]/[:property]` to return raw values of the property desired

eg `/addr/[:addr]/balance` returns the balance in Satoshis

Properties supported are
* `balance`
* `totalReceived`
* `totalSent`
* `unconfirmedBalance`

I am keen to see other properties added eventually, particularly `unconfirmedTotalReceived`, however these are slightly more involved than just pulling existing properties from the `Address` object and will be subject of a different pull request.

There is some amount of code repetition, however I figured since it can't be assumed all properties will fit into this 'template', it's best to keep them isolated so when other properties are added there isn't some code 'in template' and some 'out of template'.

I have manually tested this, but could not find an appropriate place in the `test` folder to add tests.

The motivation is that often the whole json response is not required by clients, and this approach saves bandwidth.