refactor SchemaData into AccessTable with factory

first part of the refactoring for the SchemaData and SchemaLookupData
classes. Both now inherit from AccessTable which provides common methods
and t

refactor SchemaData into AccessTable with factory

first part of the refactoring for the SchemaData and SchemaLookupData
classes. Both now inherit from AccessTable which provides common methods
and two factory methods to automatically create the correct class
depending on the schema.

Both classes no longer inherit from Schema. Instead they contain a
Schema as a member variable. This makes it possible to initialize them
with an existing schema (which is required for the factory methods).

The flow is now like this:

1: init a schema (read info from the database)
2: look at the schema to figure out if it's a lookup or not
3: initialize the right Data object with the schema

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Create an assignment for bureaucracy pages

SPR-521, fixes #100

Use DokuWiki new autoloader for class files

No longer do we need to register our own autoloader. Namespace had to be
vendor prefixed.

Added struct_schema bureaucracy type. #19

first go at bureaucracy support #19

This only implements singlge field, not whole schemas, yet.

This has no unit tests yet. Testing will be complicated. I'll try to
figure something out.