Tidied namespaces

The base namespace in some instances was PoliceUK (containing a
capitilized UK), however I changed this to PoliceUk to confirm to the rest
of the code.
Added StreetLevelCrimeAvailability call with tests

Added the call for the Police UK's StreetLevelCrimeAvailability which
closes #2.

I also tidied numerous namespaces.
Merge branch 'master' of github.com:FlyingTopHat/PoliceUK.NET