Use colour to show motion on the synoptic display

As a user I want to be able to see instantly whether something is in motion from the synoptic display

Rules would change the background colours of the "blocks" which are displayed on the synoptic view

== Acceptance criteria ==
1. PVs for moving things are colour according to whether they are in motion, have arrived (or have failed to reach the correct position?)

Start by locating the synoptic display implementation and the code that renders its blocks and reads PV state. Confirm how motion, arrival, and failure are represented before defining the background-colour states; done means moving items are visibly distinguished and the stated acceptance cases are covered.

Scritto dal modello di indicizzazione a partire dal testo della issue.