ability to mute user from post

[roadscape]

Currently, the only way to mute a user is to go to the role editor and add an entry. Need to simplify the most common use case: a moderator wants to mute a user directly from a post they see.

• The existing "Mute" button on Posts/Comments should be renamed to "Mute Post".
• Next to it we need a new "Mute User" button which will bring up a confirmation dialog for a "mute user" community json_op. The dialog text should read:

  Muting a user will automatically mute any new posts/comments they create in this community. This action will not affect existing posts/comments.