Use a store for business logic; components should handle display logic

## What is the problem?
At present, nearly all the business logic is stored in components. This was the right choice when the application was small, but as the application grows it makes more sense for the business logic to be written elsewhere. It's critical that developers agree on an application architecture so that we're working towards a common goal.

## What is the impact?
When business logic is written into Vue components it's impossible to reuse elsewhere. For example, if business logic is written into the header bar, it can't be reused by the footer -- they're two different components. The impact is that our code is less flexible.

## Proposed solution
Components should be used only for display since they represent a location on the page. Business logic should placed in the Pinia store so any component can display the data it needs.

Some might suggest that business logic should be placed in Vue "mixins" instead of the Pinia. While it's true that mixins allow some code reuse and it's definitely better than placing the business logic in components, mixins don't save state. If the header and footer components, both need to display the same data, the mixin would need to retrieve the data twice.

By using the Pinia store both the header and footer can share the same data and both can be instantly updated when a user clicks a button (an event) that mutates the state. (I'm using header and footer to illustrate components that physically separated from each other. There are better examples of components that are physically separate but need to share the same data, but a detailed knowledge of the application is required).

@severinbeauvais and I have been discussing the benefits and drawbacks of different architectures.