Provide a UI for mass unfollowing and following of issues

Problem/Motivation

Follow-up to #2183009-6: Please delete all my D6 and D7 follows from the core queue

When needing to follow or unfollow many issues, it is tedious to do it loading each issue and clicking on the button.
Following and unfollowing are non-destructive changes to issues and will not bother other people following the issue.

Proposed resolution

Provide a UI for mass unfollowing and following of issues.

a) a VBO like interface with checkboxes on the result of something like the advanced issue search
a) i) include something that will check all (on all pages) of the results
b) some simple UI for: unfollow everything
b) i) Not sure if follow everything makes sense, maybe that could reference the notifications in the profile which subscribes to all issues in the queue (which would give notifications for issues that will exist but do not yet)

Remaining tasks

User interface changes

API changes