Implement Sidebar main screen and setup for other screens

[tekkeon]

Overview

This PR implements the initial main screen (controller) of the sidebar and sets up other screens. The specific top-level changes for this are:

• Sidebar open and close events for observer emitters
• Change the header to allow for different actions or no button at all
• Allow the queue component to either display full queue or a specific number of items either from the beginning or from the next up song
• Move scroll styling to a Scrollable component in the UI lib
• Setup Session context
• Setup other screens/routes needed for the sidebar
• Make queue on main page responsive vertically