A Prosemirror based Text editor

We have replaced the Draft.js based text editor with a new one powered by Remirror and Prosemirror.

Since Prosemirror is heavily regarded in the text editing domain, we are hoping to get the following out of this change.

1. Easily extract HTML from the Prosemirror based documents in order to generate meta tags and text snippets out of the saved content.
2. Avoid vendor lock-in by using a format which can be easily converted to plain HTML or other formats.