Poll plugin: hide unused parameters / features

Recently, the poll plugin was changed such that the poll catalog component allows the selection of a poll document rather than a folder containing poll documents (HIPPLUG-1076).

Since the document picker is constrained to poll documents, the old poll-docsClass parameter is no longer useful, in fact, it may break the component when set to a different value. Also, it is to be determined if the old poll-pollCompoundName parameter is still used. Maybe such unused parameters can be hidden from the CM's component parameter dialog? On the poll document side, the "active" flag no longer makes sense.

With these changes in place, the plugin documentation should be revisited. Previously, the poll plugin was very versatile, but apparently, many of the options were hardly used. Now, it is much more to the point, enforcing a best practice. The documentation should then focus more on that best practice and less on the plugin's old versatility.