[TASK] Getters for files/images in event domain model

New getter methods are introduced in the event domain model for
getting the Extbase file reference domain models instead of the
cz_simple_cal file domain models.

The original methods getFiles() and getImages() are marked as
deprecated.
[FEATURE] Repository method for finding latest events

A new method is available in the EventRepository that returns the
events with the newest tstamp.

For the tstamp property to work properly is is added to the TCA
as a passthrough field.
[TASK] Restructured renderData handling

The renderData is now generated by the renderData view helper. The
configuration of the renderData generation is restructured.

The configuration for generating the data is now below "renderData".

The content object rendering definition is moved outside the settings
configuration to a new section called "rendering".
[TASK] Updated itemsProcFunc path and class name

The FlexForm configuration for the switchableControllerActions
now uses the new namespaced class Tx\CzSimpleCal\Utility\FlexConfig.

The invalid old filename is removed from the configuration.