Refactor languagelookup.json

[ivanistheone]

Refactor:

"nv":{
    "name":"Navajo; Navaho",
    "native_name":"Diné bizaad, Dinékʼehǰí"
  },

to

"nv":{
    "name":"Navajo",
    "alt_names": ["Navaho"],
    "native_name":"Diné bizaad",
    "alt_native_names": ["Dinékʼehǰí"],
  },

and update all the language lookup functions to the new format.

---

Also add Tetun, see learningequality/sushi-chef-stanford-digital-medic#1