Remove unnecessary is_admin() check and enqueue admin scripts/styles only on VideoJS admin page

First I took the videojs_enqueue_color_picker function out of the is_admin() check and hooked it into load-settings_page_videojs-settings. This hook is basically "load-$videojs_admin" since the add_options_page function returns a value you can use as a hook for just that page.

After that the is_admin() check isn't needed at all since all of the add_action statements are hooked into hooks that only run on the admin side anyway. I moved the add_actions below their respective functions.