feat: :sparkles: Material Library (#1)

[WYVERN2742]

Finish implementing a simple material library for selecting and managing model material properties. (See #1)

• [x] Viewing categories and materials
• [x] Editing Materials
• Material Types:
  • [x] Element
  • [x] Compound
  • [x] Fixed HU
  • [x] Mixture
• [x] New Materials
• [x] New Categories
• [x] Delete Materials
• [x] Delete Categories

Current bugs:

• [x] New materials may not be correctly categorised until a server restart
• [x] Client may attempt to 'save' special materials
• [x] Special materials should show a brief description rather than material properties
  • Since special materials are not editable, we can just replace the editor with some text.

[WYVERN2742]

Added mixture support, not that happy with the UI but it's usable:

Adding a new element to the mixture autofills the percentage box of the new element, making it easy to create mixtures.

On the technical side; the values sent back to the server are currently as strings rather than numbers due to issues with JS floating point arithmetic.

[WYVERN2742]

Unfortunately due to the refactor, this is taking longer than expected

[WYVERN2742]

Now able to delete materials, categories are automatically cleaned up when all child materials are deleted. Files server-side are also replicated correctly.