save revision and submission history of comments

Currently, Gitcasso cannot save drafts - as soon as a tab is closed, the draft is lost.

The sketch of the proposed feature is below:

- if the user has opted-in to draft saving
- then we save the draft history of their comments in a local `IndexedDB`, with a storage model similar to Gmail
- all comments are saved forever, or you can prune to only save the past `n` months
- you can "trash" a comment, anything in trash for more than 30 days gets permanently deleted
- you can go into the trash and delete a comment immediately

There are some things you can vote on

- **I want draft-saving** -> ⭐ the repo and 👍 this issue
- **I also want the option to opt-in to draft-saving on every textarea on any website** -> 🎉 this issue
- see also #98

No files or tests are identified in the issue. Start by reviewing the existing comment textareas and related issue #98, then determine how opt-in draft saving should use local IndexedDB. Done means supporting persistent draft history, retention pruning, trash handling, and permanent deletion after 30 days.

Written by the indexing model from the issue text.