feat(microdrop/protocol-grid-controller): add optional tooltips to column headers

[cfobel]

For example:

Ideally, this would be an optional property that could be set for each StepFields field.

Notes

This requires explicitly setting the associated treeview column header to a gtk.Label widget. However, this should be a fairly minor edit, where the following code has been tested to produce the attached image:

column.props.widget = gtk.Label(column.props.title)
column.props.widget.show()
column.props.widget.set_tooltip_text('Time (in seconds) to loop cyclic routes for.')

See here for the relevant code in pygtkhelpers.ui.objectlist.combined_fields.CombinedFields.__init__().