Inform user if that they are banned from a community when attempting to interact

[Iceblade02]

Requirements

• This is a feature request and not a bug report. Otherwise, please create a new bug report instead.
• Please check to see if this request (or a similar one) already exists.
• It's a single feature. Please don't request multiple features in one issue.

Describe the feature you'd like

Suggestion: Give the user feedback in some form, for instance a short red message appearing, "Could not comment/post/vote, reason: You have been banned from this community." when attempting to interact with a community they are banned from.

Reason: Currently a user is not informed when they or their content has been moderated.

This, combined with unintuitive behaviour when a user attempts to interact with a community they've been banned from could be improved. Votes simply don't go through after a short period of loading, whilst attempted comments and posts will appear to load endlessly.

As it stands, something very intentional (moderation) appears to the user as unintended behaviour without any clear reason.

[SleeplessOne1917]

This will most likely require an API change to handle in a way that isn't sloppy. There are 2 ways this could be done without an API change:

1. Look for one of the user's posts or comments in the community to check its creator_banned_from_community property. This could be troublesome if the banned user's posts were purged, and also introduces extra API calls.
2. Search the modlog for community bans. This would make sure to make sure that they didn't receive an unban after the ban or that the ban has expired. This will require extra logic and API calls.

I'll see if I can make the API more amenable to this usecase.