[FEATURE] refactoring for meta handling (OOP)

this pull request includes a refactoring for the meta handling.
it improve the code structure and is backward compatible to last versions because it implements the ArrayAccess interface.
the parsing of the meta part is now implemented in the meta model class.

the next steps would be to implement a page model and a page repository. the page model should get a property which holds the meta model and makes it accessible in an object oriented way.