Tests alongside code

[hisuwh]

I think we should move the tests alongside the code:

• it makes them easier to find
• easier to import the SUT
• really obvious if a file doesn't have tests
• also just to standardise the structure to follow our other packages and internal projects (Momenta, TTC and TeamPrevent are all doing this for there front end code)

Also then build all the test files into another directory to keep the working directory clean.

Example of tsconfig setup: https://github.com/NewOrbit/redux-authorisation