Automatically select first presentation state if none is specificy via URL search parameter

[hackermd]

Resolves #115

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 3e8739c):

https://idc-external-006--pr119-enhancement-autosele-axgwztt3.web.app

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[dclunie]

Looks good; reset (to default) also works as expected.