#73 Save dates with the categories

[StephenH]

Enhance categories database table to include:

a) Last date updated
b) Last date backed up
c) Last date restored

Then, you can show the dates during restore, and also
show which ones (user or backup file) are different
from each other, which ones haven't been backed up,
etc.

These should also be shown if doing a trial restore
(where you don't actually restore anything --
different feature request).