Adds Ctdbp transforms for pathfinder

* Adds the CTDBP L0, L1, L2 salinity and L2 density transforms.
* Note that there is one L0 transform, one L1 transform and two L2 transforms.
* Adds integration tests: one each for L0 and L1, and another integration test which links L0, L1 and the two L2 (density and salinity) transforms together in a chain and checks that the granules published by each is the right kind.

* For the test, we are using fictitious values of calibration coefficients. If we later know about the calibration coefficients used in the real world, maybe those could be imported later for the test. Note that these CTDBP transforms are not going to stay for long. They are only for the pathfinder. Pending changes to the transform structure, they might be replaced.

* What may be added later is more assertions to check that the algorithms have been performed. So far we are only checking that the granules published by each transform contains data for the appropriate parameters.

* Also, in test_ctd_transforms.py, there were lines that were unnecessary, so they have been removed.