Revert "Refactor docs/sources to reflect css change to extension status"

This reverts commit adcf9fff6bf8c31a780aae19ee9e4cd3f4470f35.

Conflicts:
	doc/en/user/source/extensions/index.rst
[GEOS-5903] Link to CSS reference in the css demo page does not work
[GEOS-5906] Gathering attribute statistics in the CSS demo page should be optional