Fix poor interaction between sf.css and Foundation

Foundation CSS specifies a "table tr th" selector, which is
more specific than "table th" and thus gets chosen. But it
has dark text on a light background, whereas sf.css is
specifying a dark background for <tr> elements. The result
was unreadable dark text on dark background. Making the
sf.css selector more specific ensures that it will be chosen,
thus making table headings look good again.
Rename "result" to "record" in userdata template

This avoids confusion with the variable named "result" in the
parent scope.
WIP on admin CRUD: Update is working now

This still has a bug: it will obliterate any fields not in the
PHP user model, which notably includes the password
field. Since I don't think we want to be passing password
hashes back to people's browsers, that means we need to
tweak the user model to use $set: {"fieldname": "value"}
rather than just updating the record as-is (which, in
MongoDB, will just overwrite the record and obliterate
any fields in the "old" record that weren't in the new one).
But that's an exercise for later.
Swapped order of columns in user list table

It makes more sense to present the username, rather than
the email address, as the "primary key" to be clicked on to
edit an account. ("Primary key" in quotes because it's not
the *real* key, which is the ID field that's hidden from the
end user.)
Added add and delete buttons to user list

They're not yet functional, but this gives me a sense of
where they belong in the design.
Added nonfunctional sorting buttons to user list

Again, these are nonfunctional but give me a feel for how
the design will look.
Refactor: get rid of old testing code

The $scope.data.message variable was only used for my
initial testing of Angular data binding. We don't need it
any longer. I'm also moving around the call to fetchUserList()
and the initialization of $scope.vars; they make more sense
coming right after fetchUserList() is defined.
Implement delete button for user list

The delete button is now functional.

Note how the ng-class directive is conditional. I learned that
trick from http://stackoverflow.com/q/7792652/.
Implement add button for user list

That's it; that's all it took: thanks to Mongo's "upsert" feature,
we could re-use most of what we did for updates.

The button layout is a bit unintuitive at the moment, and
could probably use a redesign. Maybe the "Save" button
could change itself to "Add" in a context-dependant way?
That's a thought for later.