Want to be able to limit Olark Chat from displaying for particular user roles

As an administrator, I wanted to be able to prevent Olark from displaying for this particular role. I felt that people who use this module on their sites, they might like to prevent Olark from displaying from their builder or contributor roles as well. This patch that I made adds the list of roles on the admin settings form, and any role checked off have the Olark Chat module not displayed for them.

Another functionally that I did not add, but could be useful, it turning it off based on path, similar to how fckeditor allows you to add/remove it on certain paths. Just a suggestion.