PanPhon link to base data

[LinguList]

panphon has a list of about 6000 segments (some redundant) linked to a feature set:

• https://github.com/dmort27/panphon/blob/master/panphon/data/ipa_all.csv

It would be useful to also link those. The features are interesting, and the IPA is close to the one we employ.

[LinguList]

With PanPhon linked (will PR later), we have 7480 different sounds, but PanPhon has already ~6500 different sounds (many aliases, though).