Adding utests on GDALCommandLine

TODO: not sure on what to test actually, it might be improved, need to
see with @jeichar.
Adding tests for ScaleUtils
Adding tests on Tab extraction

(MIF format to come)
Changing doc in WcsReaderRequestFactory

TODO: still need some improvements
Adding a test for extracting as MIF format

Note: this format is broken, so the test is currently marked as ignored.