Removed dispatch, use spray for ArgUrl reading.
Fixed ArgUrl tests.

Using a spray server in a test suite was tricky, ended up having to use only one instance of it for the test suite using BeforeAndAfterAll.
Moved the gtloader project out of this repo.

You can find the python-geotrellis package, which has this gtloader code, in the python-geotrellis repository.
Changed version to RC4