Display correct timestamp in messages and contact list

Got some inspiration from briar-headless for the contact list:
https://code.briarproject.org/briar/briar/-/blob/release-1.3.8/briar-headless/src/main/java/org/briarproject/briar/headless/contact/ContactControllerImpl.kt#L81

Closes #53.
1 job for !23 with 53-timestamps in 3 minutes and 53 seconds (queued for 28 seconds)
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