Fix removal of recurrence rules in exceptions of recurring events

[sunkup]

Purpose

Obsolete recurrence rules were not being removed from recurrence exceptions properly. This happens due to repairing single events right away, before "knowing" their exceptions. With this PR "removal of exceptions" is done only after all events have been created with all known exceptions. That is any repairs are done after completely reading an iCalendar and before writing.

Description

• [X] alters tests to cover usage of EventValidator.removeRRulesOfExceptions() in Event.eventsFromReader().
• [X] applies EventValidator.repair() only after all exceptions have been found - after completely reading an iCalendar
• [X] adds more documentation to EventValidator
• [X] renames repair() method to validateAndRepair()

[rfc2822]

It might be cleaner to repair all events at once, after all the exceptions have been found, before returning them in Event.eventsFromReader().

👍🏻 The Validator should be kind of an interface that validates and repairs events, but the calling code should not know details (like that it deals with rrules of exceptions or whatever).

So we should only expose the repair() and call it at the right time:

1. after completely reading an iCalendar
2. before writing an iCalendar

(which should be documented in KDoc of EventValidator)

Because we can't do everything we need from fromVEvent(), we should call repair() when the complete event is available. And then we can adapt the tests, too.

Would love if this PR would not only fix the issue, but also make event validation a bit more documented.