Add hook service for registering callbacks

This may be used by plug-ins to register callback for hooks defined in the core.
Load additional JS files via hooks

This enables plug-ins to load directives that are used to format WP properties.
Receive directives from hook and render them

This allows plug-ins to apply specific formattig to WP attributes that are not handled otherwise.
Add HookService tests
Test plug-in properties in overview
Allow plug-ins to set displayed properties
Adapt tests to missing default WP properties
Merge pull request #1733 from opf/feature/14005_show_costs_attributes_in_overview_tab

[Feature] 14005 show costs attributes in overview tab