Patternfly Table view element support, Column Visibility

[mshriver]

https://www.patternfly.org/pattern-library/content-views/table-view/#design

There are several patternfly widgets that are part of the table view markup, including column visibility.

Satellite QE, specifically the Airgun team, will have a future need to model this widget for automation.

Currently the MIQ/integration_tests team has implemented a conditional view for the patternfly content views:
https://github.com/ManageIQ/integration_tests/blob/master/widgetastic_manageiq/__init__.py#L2826

This can be adapted and extracted into a base ContentView class within wt.patternfly. Support for the table's column visibility checkboxes should exist in this library.