Revert "Implemented EZP-19411: Avoid file_exists and include calls for registering datatypes and workflows"

This reverts commit a6bfaa622342b728951c7f45bb066828440c3be3 as introduced in #344

This change broke SetupWizard (actually the changes to extensions did) and there are also reports from
community about fatal errors, mostly likely because own settings (override/siteaccess/extensions) specifying enabled datatypes.

We will do a second try on this improvment in a way that does not change the behavour of the setting (suggested: setting[<new:class>]=<old:value>)
For further discussions see issue: https://jira.ez.no/browse/EZP-19411

Conflicts:

	doc/bc/5.2/changes-5.2.txt