updated version number to 1.5.4
Revert "updated version number to 1.5.4"

This reverts commit 78635848ff80b65150b6cd5bb17ce97257f8e689.

was only committed as a test
added type names to comments and type hints to function signature
repair module for page zones whose inheritance has been damaged by bug #2134
added a unit test stub for SectionModuleController::changeParent()
added unit test stubs for PageZone::inheritExtra()
guard against test fail if export_html script is not present
typo: the inherits_from attribute is in and stores the concrete page zone (id), not the abstract page zone [#2134]
cosmetics [#2134]
set up a hierarchy of page zones to test inheritance [#2134]
Merge branch 'master' of https://github.com/opennewspaper/opennewspaper into #2134