User preferences - show suppressed records

[Delivers #39233355]
Introduces user preferences and the first preference - whether to show suppressed records to those who have permission to see them. Previously suppressed records would appear in browse and search lists. Now, by default they do not. Users can choose to show suppressed records by editing their preferences record - under the system menu.

It's a bit daft having all this stuff simply to present a lonely checkbox, but there are other preferences coming - like browse columns, etc. So this is a simple case to get user preferences out there. There is some hidden complexity and there are some unresolved issues that are not exercised by this simple case.