Dashboard: load a default rather than starting new

[LuudJanssen]

Closes #5820
Also did some code cleanup in the files I was working with.

[ghost]

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[spalger]

I would prefer that we didn't have a route for /dashboard/new. I think we should simply be redirecting requests from /dashboard to /dashboard/:id if a default dashboard is defined.

I think we should instead use a query string to tell the route handler for /dashboard that we are not interested in redirecting but definitely want a blank dashboard, something like ?create=true or ?default=false.

[ghost]

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[rashidkpc]

Haven't seen any feedback from the submitter, closing to clean up list. @LuudJanssen please feel free to open a new pull if you'd like to address the issues above. This looks like good functionality that just needs some small changes