Making the Api library testable

[LuckyNoS7evin]

So the Api is not really testable at the moment due to its dependency on HttpClient (>2.0) and WebRequest (<2.0)

Therefore I propose the following:-

1. Break out the actual calls made into a different class
2. create an interface
3. profit

With the aim of making the Api more DI friendly this would mean a new constructor value in which a "HttpCallHandler" can be injected

[jaybyrrd]

We should probably create an issue for each section so that people can work on these independant of eachother. I know there is a pr out there setting the baseline for this.

[LuckyNoS7evin]

good shout, at the moment we have a few helix ones in there...