Styling and onboarding

* Added a footer (it has to be outside all of the content) https://github.com/Eduki/eduki/issues/146
* New styiling for premium page
* Hovering for icons on the enrolled courses overlay https://github.com/Eduki/eduki/issues/147
* Better onboarding message for if a user doesn't own courses or have enrolled courses https://github.com/Eduki/eduki/issues/143
* Favicon (it doesn't show up in my browser, only in like bookmarks, etc.) https://github.com/Eduki/eduki/issues/150