New types and state management

[gskorokhod]

Goals

• Switch from interfaces to classes, with proper encapsulation etc
• Have one State object that can be passed to components and encapsulates looking up objects by UUID and CRUD operations on them
• Make the new types serializable to JSON and back
• Ensure consistency between the 3 states that we have in the application:
  • In-memory instances of objects
  • The Svelte global store
  • Serialized data in browser local storage

ToDo

• New types for Person, Location, Task, Skill, Assignment
• Some documentation
• New State object
• Update the core UI to use new types
• Update data table components to use new types
• Clean up code & imports
• New Generic components

[gskorokhod]

this took... way more than expected but I have now updated the core UI to use new types.
Shift & Assignment UI is being redesigned now so I've removed it for now