Store the array of table data cells in Grid.Row.
Use row instead of oldRow as the variable name.

We're not replacing the row object, so it's not "old".
Datasources now provide row objects, not column data.

Change handleRowInsert to match.
Disable navigation buttons when they're not useful.

Prevents users from doing things that would cause exceptions, or move
to the same row that they're currently on.
Document some more things I need to write tests for.