DataHandler: Replace services by modifier

[Armin Vieweg]

Services for entity records are not flexible enough. Currently:

• it is not possible to extend a single service by own functionality
• Services are not able to get extended (like RootPageService extends PageService), properly
• The split of configuration and execution is not well implemented
• iwm show does not execute methods _applyService and _applyDataService, but iwm update does

[Armin Vieweg]

Services has been replaced by modifiers now. Modifiers are classes in PHP, which implements some interfaces. These interfaces are used to limit modifiers for matching entity types.

A modifier for sys_template will fail for a page, e.g. because the properties are not necessarily the same.

Services are still existing, but with a complete other meaning. They are slots which can be connected with signal "EarlyOperations", called in Environment::apply() method.