Extend modes of the JAMS key_mode namespace

[andreamust]

Original datasets may have different convention for annotating the track's key, compared to the JAMS's library key_mode namespace, which only defines a few modes, namely:
major, minor, ionian, dorian, phrygian, lydian, mixolydian, aeolian, locrian.

Datasets like weimar, instead, include modes like chromatic or blues.

Due to the difficulty of finding a good alternative for the non-listed modes, it would be needed to create a more comprehensive key_mode namespace.