Preliminary implementation of the interpolation extension.
Implemented WCS 2.0 interpolation extension.
Updated autotest.
Fixing typos. Implementing interpolation value selection for mapserver.
Updating tests for interpolation.
Updating expected results
Assuring that all interpolation methods are lower-case.
Merge branch 'interpolation'

Conflicts:
	autotest
	eoxserver/services/mapserver/wcs/coverage_renderer.py
Merged autotest.