added dashboard to demo LOConnection and helper utilities

[bradley-erickson]

• [x] Needs documentation

[bradley-erickson]

• [x] Add ability to manually call open and close on the websocket

[bradley-erickson]

• [x] Data manager component needs testing now that #162 has been merged in

[pmitros]

Where we might be headed:

import { someStuff };

export function myComponent(data) {
  // When we need to add some interactivity, it might be a line like:
  const dropdown = useLOConnection(query);
  // ...
  return (<>{data}</>);
};

// Syntax below would be different.
//
// Perhaps we'd want a standard way to define display modes
myComponent.displayModes = [latestGrid([some stuff]), // All students current work, for the whole class
                            assignmentSingle()];      // Select a student and assignment from a dropdown