removed unsupported config options from configparser

those were remains from other output modes in the data plugin but are
not yet supported in struct

fix config parsing of multiple schemas

output the key not value for unknown option in ConfigParser

properly parse width settings in aggregation table

makes sure only valid CSS values are supplied

Use DokuWiki new autoloader for class files

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

Enable sorting by mutiple columns

default to translated column labels in table aggregation

This also fixes errors that where thrown when headers were not
specified.

Render output tables with data-like syntax

ToDo: summarize

Correctly initialize $this->config

no array constants in older PHP versions

began work on the syntax component to aggregate data

This copies over a lot of configuration functionality from the data
plugin, but is still missing the functionality itself.