Store requests by UUID instead of URL

fixed an issue where certain GET requests would be performed more often then needed and added tests for the requestservice (not everything tested yet)

Replaced Http with HttpClient

Closes #150 

Switched to storing requests based on UUID, generalized UUIDIndexReducer to work with any type of index

cleaned up remotedata for a better separation of concerns, moved statuscode and errormsg in to RemoteDataError object, moved pageInfo to PaginatedList object in the payload

Increase test coverage