move properties to their own page

stage work to simplify v7+ doc work
restructure directives
Merge branch 'v5-stable' into v7-stable
improve property doc
remove content-less expression document
Merge branch 'v5-stable' into v7-stable
add config principles
Merge branch 'v5-stable' into v7-stable

Conflicts:
	source/configuration/basic_structure.rst
slight adaption to v7
Merge branch 'v7-stable' into v8-stable