Reorganise services

Services were a big mess before. I've attempted to enforce some kind of order.

## Common API
The **BBC Services** and **My Music** service providers had completely different interfaces. They've now been standardised.

## Services Register
This object accepts service providers and keeps track of which provider is responsible for a particular service. It routes requests for metadata to providers.

## Services Manager
Emits data about registered services and handles service alterations.

## Tests
Remember them? I done wrote some.