[!!!][TASK] Automatically exclude Extension tables

When an Extension table is connected to a content or a plugin type
in the registry this table will now also be excluded from refindex
traversal by default.
[FEATURE] Register multiple content type tables

The method registerContentForTables() is added to the
CacheOptimizerRegistry to allow the registration of multiple tables
to a content type with one call.
[FEATURE] Default config for Extensions

Default configuration is added for the cz_simple_cal and the
news Extensions.
[BUGFIX] Clear plugin cache of excluded tables

Since the table exclusion should only prevent refindex traversal
the related plugin / content cache is cleared before the
further processing is skipped when a table is excluded.
[TASK] Add documentation