Replying a comment.

Commenting UI: https://zpl.io/brBk9eW

As a logged-in user,

When I am on the feed section and I see a post, I should be able to interact with the post, and also the comments on the post.
I should see a clickable "reply" text on all comments and should also be able to click on the "reply" text on any comment that I want to interact with, and that should open up a text box to type out my reply, I should then be able to send the reply off after typing and the replies should also be visible to other users.

Design link: https://app.zeplin.io/project/5ec4729feee8e847b8d9f1d1/screen/5ee53a05f7dcfcb2acc17108

Acceptance Criteria
Users should be able to see clickable "reply" text on all comments, and when they click on any, users should be able to type out replies to comments on any post in the feed, send it off, and the replies should also be visible to the other users.