comments: Add proposal author updates.

[amass01]

Spec

Proposal authors need to be able to give periodic updates on the status of their proposal. These updates will be given as comments. The Politeia users will have the ability to interact with the author and ask further questions.

Currently, once a proposal vote has finished the proposal is locked and no additional comments can be made. The new behavior will be the following.

• Once a proposal vote has finished, all existing comment threads are locked.

• When a proposal author wants to give an update they will start a new comment thread. The author is the only user that will have the ability to start a new comment thread once the voting period has finished. Each update will have an author provided title.

• Anyone can reply to any comments in the thread and can cast upvotes/downvotes for any comments in the thread.

• The comment thread will remain open until either the author starts a new update thread or an admin marks the proposal as closed/completed.

implementation

• Each update will be shown as its own comment section. The updates will be displayed from newest to oldest.

• Each update will have a title.

[amass01]

I'll be working on that.