Removed localStorage save but added an option to collapse groups on load

I decided to remove the localStorage thingie. It adds some extra complexity that I feel is not worth the trouble. If someone really think we should keep the current sidebar state in localStorage, please feel free to ask.

Although I added a way to collapse all groups on load. This is done through the `initialSidebarCollapse` option (boolean). If someone has a better name for it, please share. :)