Bug Fixes, UI overhaul

[iris-liu0312]

New Features

• Even more informative errors: tells user how they might fix an error.
• Participants nodes are replaced by Entity nodes, with participant role names placed in edges.
• Overhauled the navigation bar with MUI components for a sleeker look.

Bug Fixes

• Duplicate edges in back end processing are removed.
• Flat schemas can now be visualized.
• Centering issue is temporarily fixed by preventing automatic centering.
• Root nodes and schema name are found through hierarchical edges as opposed to previous temporary solution.

Known Issues

• Nodes reposition themselves whenever the graph is expanded or collapsed.
• Entities, participants, and relations cannot be changed through the sidebar.