Documentation structure harmonized (issue #781) (#800)

* Documentation: formatting fixed.

* Documentation: PRO contents copied here.

* Documentation: SCTunit documentation excluded for now.

* Documentation: build process fixed.

* Documentation restructuring (issue #781)
* Restructuring done
* Changes for Eclipsehelp done

* Documentation restructuring (issue #781)
* Changes for Hubspot done
* Minor text changes

* Documentation: Hubspot footer change incorporated.

* Documentation: website-specific stuff renamed.