feat(rxStatusColumn): Add support for coloured status columns

This provides `rx-status-header` and `rx-status-column` attribute
directives, used to modify `<th>` and `<td>` elements for the purpose
of showing coloured statuses in one column of a table.

You can define mappings to go from your own internal status values
to the four currently provided by the framework.

Closes #688
I was kind of hoping for a joke here. `If you ask it to map a string, it will tell you that the shortest distance between two points on a sphere is not a straight line, but a great circle (a type of geodesic).'