Activity data changes: interface cues

[tmillross]

An option for tracking data changes, as related to #10.

1. All modified cells are colour-coded (a border or fill in a different colour to the default non-edited cell colour).
2. Colour change is maintained until panel or AB closed.

For example:

• edited value in a table = yellow cell border
• edited description text field = yellow cell border

Notes:
a. Should be clear and consistent.
b. Some information could be provided to inform user that this is standard AB behaviour.
c. A bit of research into design / usability / human-computer interaction would be worthwhile to choose the optimal colour mix.