Pronouns moved to a separate file

[al-muammar]

Summary

This PR fixes #23 which is a redundancy that we currently have. All pronouns (except i and we are coded with first letters of their grammatical features. For example: singular, dual, male = sdm It significantly decreases verb-forms.json.

Test Plan

Played with our test bot:

Learn Arabic Test Bot, [Feb 4, 2019 at 9:43:44 AM]:
We did

Muammar Al-Shedivat, [Feb 4, 2019 at 9:43:51 AM]:
فَعَلنا

Learn Arabic Test Bot, [Feb 4, 2019 at 9:43:51 AM]:
Well done!

Learn Arabic Test Bot, [Feb 4, 2019 at 9:43:51 AM]:
They (two women) did

Muammar Al-Shedivat, [Feb 4, 2019 at 9:44:06 AM]:
فَعَلَتا

Learn Arabic Test Bot, [Feb 4, 2019 at 9:44:06 AM]:
Well done!

Learn Arabic Test Bot, [Feb 4, 2019 at 9:44:07 AM]:
They (two men) do

Muammar Al-Shedivat, [Feb 4, 2019 at 9:44:28 AM]:
يَفعَلانِ

[rguliev]

Or we can leave it for now. Because, as I see, we will have to move to DB soon. We will just replace these codes by id and link them.

[al-muammar]

@rguliev, not entirely sure about your DB idea. What do you mean? :)

[rguliev]

I mean that eventually, we will switch to DB anyway. And in DB it will look like two tables pronouns and verbs connected by id. So, we will not need "keys" for pronouns to map verb form and a pronoun.