RF: continue MINC1 refactoring for adding MINC2

Make compressed tests an addition to a base test class; MINC2 cannot use
compressed files.

Some renaming of logic for creating loaded file from file objects.
NF: First pass at MINC2 loading with tests

Add MINC2 loading - very basic, with no save.
Inherit MINC1 tests
Add example file and check loaded parameters against mincstats