fix theme options so they reflect 2.2 and 2.3 docs

I believe #3376 was prematurely closed. I just installed a fresh version of 2.3/develop and `{{ theme:options:option_slug }}` throws an **Array to string conversion error**.

The problem here was `$this->theme->options` (referenced by `$themeOption`) **has no slug**. You are populating `$this->theme->options`, so it would never have a slug.

My loop takes all the model options and binds them to the appropriate `key(slug) => value` sets. This returns the functionality of `{{ theme:options:option_slug }}` to what is expected from the docs.