Support for pat-switch + minor optimizations.

[thet]

• Support for rendered events via some configuration options.

Plus:

• Deactivate some more event-add related code paths if not needed.
• Do not include properties not existent in the event source. Avoids problem of setting a href attribute of undefined in the calendar.

Refs:
https://github.com/quaive/ploneintranet.prototype/issues/1184
https://github.com/quaive/ploneintranet.prototype/commit/e51717c0cdc6d95ce8a2222b6453becc0fe65df1
scr-844