Import pygrid via iris.proxy for full optionality.
Skip pyugrid tests if it's unavailable.
Add nearest-neighbour interpolation.
Merge pull request #1408 from QuLogic/pyugrid-optional

Make pyugrid truly optional
Check that cube.copy() makes a fresh mask.
Tidy test code.
Doc-string correction.
Merge pull request #1419 from rhattersley/nearest

Add nearest-neighbour interpolation.
Document fast fieldsfile loading.
Merge pull request #1416 from pp-mo/scalar_cube_copy

Check that cube.copy() makes a fresh mask.
Review changes.
Merge pull request #1420 from pp-mo/fast_ff_doc

Document fast fieldsfile loading.
Chnaged naming of height coordinates in NAME trajectory output files
Update NAME file tests
Update naming/ids
corrected names and id and CML
Merge pull request #1423 from lbdreyer/name_loader_update

Changed naming of height coordinates in NAME trajectory output files
validations
ukcanext
radcloud