Add inst/extdata/zonation-tutorial to .gitignore

Just before addition of ca. 4.5 MB tutorial data folder (has only do_abf) master was branched to tutorial-data. Use this if data is needed (mostly for tests).
Add zonation tutorial data in inst/extdata

Only do_abf added.
Test that Z tutorial data exists
Fix existance checking for curves reading
Fix default variant naming
Test Zproject and Zvariant
Fix generic plot method definition for Zvariant
Fix normal groups legend name in plot
Fix group plotting
Add Zonation tutorial data
Merge branch 'tutorial-data'

Conflicts:
	inst/extdata/zonation-tutorial
Re-add tutorial data
Remove tutorial data
Rere-add tutorial data
Check passes
Bump up the version number to 0.1.1