Add domain and interfaces

Add the following:
-  a domain object representing bike shops.
-  an interface to get bike shops in a boundary box
-  a skeleton implementation for the interface, using CycleStreets
-  a few unit tests.

Some things to be completed in subsequent PRs e.g. making the UTs `MainActivityTest` and `CycleStreetsShopLocationServiceTest` actually meaningful.
Might be worth having a look at the retrofit library for this, it lets you treat remote REST services in a similar way to spring data interfaces.

https://github.com/square/retrofit