Class tree rendering and miscellaneous improvements

[LunaY0Yuki]

Some of the bugs/improvements of the tree:

• When a user creates a resource and the resource modal closes, the new resource does not appear in the tree.

• The URL for the tree is not working. When the tree is at a specific node, and the user reloads the url, the website shows that the page is not found.

• When a user right-click on "All Classes", the menu should not light up "Add" because you cannot add a new resource to the root of the tree.

[LunaY0Yuki]

In order to animate a new resource appearing in the tree after you create it, we might need to call a function in the Tree class as our success callback function.

But... right now because the resource modal is just a bunch of functions, it's really hard to pass a reference to the Tree object around.

So... actually we might need to rewrite the resource_modal.js as a class.

[LunaY0Yuki]

We don't have any UI to create classes? Right now, "add" in the context menu only add new resources.

This might not be MVP. We could just make admins create classes for now.