Worksheet List refactor: proof of concept

- Consolidate all components under one Worksheets parent component
- parent component handles which child component is 'active'
- parent component listens for keyboard shortcuts and handles them, or dispatches the event to the active child component, or does nothing if the active component doesn't care
- parent component keeps track of text to filter by, list component does the filtering at render time
Add comments to proof of concept
Merge pull request #649 from codalab/feature/worksheet_list_refactor

Feature/worksheet list refactor