Added icelandic proficiency to frontend

[17luke]

@thdg Note, requires "icelandic_proficiency" column to be added to database clips table. Note, please check my Icelandic in the localisation file (locales/isl/demographics.json)

• Asks user's Icelandic proficiency on demographic form.
• Automatically sets to "native" if mother tongue is Icelandic.
• uploadClip POST request now includes "icelandic_proficiency" in contribute-api.ts

[judyfong]

@17luke @thdg you should also check the proficiency level of their native tongue too. But more granualar: B2, C1, or C2. For example many native english and icelandic speakers are only at B2 or C1 level. They never bother getting to C2 level.

Also you should change the why this matters text in english to match the icelandic one: the more varied and multi-faceted(?) multichanging?, the better.

Finally when people are tired and have been doing an activity for over an hr their prociency at a task drops.

Finally, you should check which region the speaker is from like rvk vs akureyri so you can evaluate recordings based off of their dialectal differencies not based off of absolute correctness, which is only akureyri/harðmæli dialect.

A lot of kids recordings were rejected because they ellided some sounds even though its correct and native íslensku