legacy: Comments fixes - Githubissues

This PR fixes some issues on comments section:

Lowercase edited label for edited comments
Remove "See raw markdown" from censored proposals, and show it only when proposal has an index.md file.
Display comments for vetted censored proposals
Show "What are your thoughts?" message only when new comments are allowed
Block comment edits for threads that don't allow new comments
Show correct error message for invalid author updates replies

decred / politeiagui