Simplify app toolbar

[MetRonnie]

In #2542 we were not 100% agreed on the new icon for the nav sidebar. I am proposing this icon for when the sidebar is open:

and this for when it closed:

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This PR also includes a few changes to eliminate technical debt that I had gradually accumulated to the point where I think we should get them in.

• Removing the app module from the vuex store as all it is used for is setting the toolbar title and there are simpler ways to do this
• Replacing the GraphQL mixin with a composable and simplifying data flow across the app by eliminating some props

Users coming from Vue 2 may be familiar with the mixins option, which also allows us to extract component logic into reusable units. There are three primary drawbacks to mixins:

1. Unclear source of properties: when using many mixins, it becomes unclear which instance property is injected by which mixin, making it difficult to trace the implementation and understand the component's behavior.
2. Namespace collisions: multiple mixins from different authors can potentially register the same property keys, causing namespace collisions.
3. Implicit cross-mixin communication: multiple mixins that need to interact with one another have to rely on shared property keys, making them implicitly coupled.

For the above reasons, we no longer recommend using mixins in Vue 3. The feature is kept only for migration and familiarity reasons.

Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• No changelog entry needed as invisible to users

[ChrisPaulBennett]

There is still an inconsistency between workflowID vs workflowId.
I think something is changing the case (GraphQL maybe?)
This may not actually be an issue, just thought I'd bring it up since you have altered a few of them.
Much better icons!

[MetRonnie]

I was hesitant to change the GraphQL variable $workflowId but actually the variable name doesn't matter - it won't break anything. Changed to $workflowID now

[MetRonnie]

Ping @samuel-denton are you happy with these icons for the sidebar toggle button?

[samuel-denton]

Ping @samuel-denton are you happy with these icons for the sidebar toggle button?

Yep I like those, consistent with everything else.