Remove duplicate code ��

The functions \action_plugin_struct_entry::createForm and
\action_plugin_struct_entry::makeField are duplicated in
\action_plugin_struct_edit

made Assignments singleton. fixes #163

adjust tests

fixed last tests, removed old validator

first test for new Dropdown features

fixed tests

renamed tests

renamed SchemaData and SchemaLookupData

This is to reflect that they no longer inherit from Schema

fix all the tests for the recent change regarding SchemaData

I'm not to happy with the SchemaDataNoDB class and its use
SchemaDataSQL.test - it seems hacky, but works for now.

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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saving lookups works

drop the compare() function in favor of filter()

Create explicit columns with types now needed

method signature adjustments in mock objects

fix and test placeholder replacement

test that left joins are positioned correctly

Use DokuWiki new autoloader for class files

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

adjust cachung if an aggregation depends on dynamic values #75

support for dynamic filter place holders #75

tests for struct stuff still missing
no cache handling, yet

allow validation to modify the value before saving

moved validation to its own class

the validator class is partly test covered through the entry tests but
dedicated tests might be helpful

Add/adjust tests for changed filter handling

See commit 9dbc32ae40e6ae835e9edeee14fdde77ad1c59f3

added tests for testing translatio initialisation #35

moved mock objects to their own namespace #35

we may want to reuse them in different tests