Remove 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` instead. 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.