This change breaks compatibility with comments API of previous
JSDuck release.  But the only effect of this is that the Users and
Targets lists on comments index page will be empty, so I consider
it OK to make this change as it will only make the comments index
page a bit less useful while the transition happens, but won't
break anything badly.

Rename Comments.getAllTags to .getTopTags, so it's in line with
.getTopUsers and .getTopTargets.

Ensure tags are sorted alphabetically in TagEditor (the backend
now returns them sorted by comment count).

For now the comment counts aren't shown in tags menu, but otherwise
it's working.

For now the list of tags is completely hardcoded.

Send tags along with comments from backend.

Render the tags in comments template.

Improved stylesheet for rendering all the items in top-right corner
of each comment.

For moderators, also render the add/delete buttons for the tags.

Implement the tags in nice relational fashion, but set up triggers
to avoid quering the tags table with each select of comments, and
instead precalculate a textual tags column inside the comments
table.

Also added a migration script.

Just rebuild the entire total-comments-per-class cache.
We could do it in a smarter way, but as it only needs to be
done when posting/deleting comments, it happens rarely enough.
And the performance is actually just good-enough; no noticable lag.

Use the common Comments.avatar method to generate the <img> tag,
giving us the same default avatar that we use everywhere.

Also toggle the subscription checkbox depending on the status
of subscription in commenting form.

The guide config can now contain an "url" field which by default
points to guides/<guide-name> but can be configured to point at anything
desirable.

Remove an old restriction left over from the days when JSDuck didn't
show private members at all.

Only when the enum is an auto-expanded list of alias values
or when it's defined as array - only then show the warning.

The :config_file task generates initial simple sdk-vars.rb config.

The :configure runs both :get_extjs and :config_file, doing the
initial setup for running jsduck.

This should help tools like readability.com extract the contents
of the page.