Merge pull request #16 from discordier/develop

Add support for sub select palettes mentioning legend names.
Merge pull request #17 from discordier/unit-tests

Add unit tests.
Merge pull request #18 from discordier/extend-palette-fix

Extend palette fix - including test cases.
Fix: recalculate the palette condition for extended palettes derived from default palette.
Remove code redundance: recalculate only in one place.
Merge branch 'fix-palette-condition' of github.com:discordier/contao-meta-palettes into fix-palette-condition