Further diagram guidance within the style guide

[Blueskies00]

A couple of points I've come across when following the style guide for diagrams while working on the nominee page that would be useful to have clarification on.

• Clarification over when icon labels (e.g. Person A) should be included
• Guidance around the background rectangle sizing (e.g. should all rectangles in one diagram be the same width, or by row, or by statement type, or simply by text content)
• Guidance on when text should sit on a new line (e.g only when exceeding the box width, only for separate fields)
• Guidance on what takes precedence - box sizing or font sizing

Of course, as we cover more complex topics in the documentation these may need to flex, but a starting point would be useful for consistency.