Events with 'repeatFixedDates' should not modify startTime and endTime of events and handle date and time format

 Restore the events startTime and endTime properties after generating the 'repeatFixedDates' recurrences,
 otherwise following regular recurrences are affected (moved to wrong days and times).
 Calculation of start and end time did not work when using time format other than H:i:s.
Merge pull request #8 from thkuhn/hotfix/repeat-fixed-dates

Events with 'repeatFixedDates' should not modify other events