Fix specifying multiple classes with addclass

We support adding multiple classes depending on a single keypath with the syntax `data-addclass-foo|bar`. However, due to the way it was implemented, it wasn't working.

This also cleans up the class name whitespace, so that after multiple togglings we no longer get node class strings like `btn___toggled________active` (where underscores are spaces).

Paired with @xthexder

@ibawt @SoapyIllusions for review