Add support for class (@) folders

[cafarm]

Per Khris:

I've found myself desiring a specific enhancement where Symphony would support class folders.
If anyone else wants it, here is the change I've made on our local machines. It doesn't require recompiling Symphony-core so I've just modified our Symphony installer (.mlappinstall) rather than repackaging it. Obviously, this will revert if an update comes out.

The original line (74) is:
elseif ~isempty(name) && name(1) == '+'

And I've changed it to:
elseif ~isempty(name) && (name(1) == '+' || name(1) == '@')