Add timestamp (format 10 Jan 2023) to root element of chain display (uses today's day at the moment). #52 deals with replacing that with date of root event time.
Cosmetic improvements: use dart library for timelines to connect tick boxes next to chain elements.
Closes #14
10 Jan 2023) to root element of chain display (uses today's day at the moment). #52 deals with replacing that with date of root event time.