Diagnostic refactoring

[Modularius]

Summary of changes

1. General refactoring to make code more idiomatic
2. Moved the constructor and display functionality of DigitiserData to its own file.
3. Reworked the column structure to group up related items (as described in the README).
4. Added weights options to the column widths, making some columns larger than others.
5. Introduced Channel column which monitors a single channel (adjustable with left/right keys) and displays channel id and sample range.

Instruction for review/testing

General code review.
Test with command such as

cargo run --bin diagnostics daq-trace --broker 130.246.55.29:9092 --topic daq-traces-in --group vis-3

when a run is in progress from the chosen broker.

[DanNixon]

👍