Declare extension a beta-version

- add new timer jewishHolidayTimer, which allows periodical content related to jewish holidays, and define some unittests
- refactor rangeListTimer and define some additional unittests
- refactor periodListTimer and define some additional unittests
- remove small bugs
- add viewhelper timer:jewishDate, which can transform a normal date into the date of the jewish calendar
- declare extension as beta-version
- refactoring of code by using phpstan (level 6) and phpcsfixer