Additional Selector tweaks and test cleanup

* Use late binding for better extensibility
* Tweak name and type of 2nd argument to renderSelectorInput
* Move selector check outside of _configureSelectorColumn
* Add flag to avoid needlessly calling _updateHeaderCheckboxes
* _changeInput -> _changeSelectorInput
* Minor reformatting
* Update remaining instances of selector: true to "checkbox" in tests
* Remove grids in test page showing spurious use cases with checkbox + radio
Tweaks to Selector docs
Update docs based on latest wiki content and 0.4 changes