Fix wrong total work time in month with less than 31 days.

timeHelper.timeToJsDate created times with 1899-12-31 as date. We then set the
year to e.g. 2013 (2013-12-31), and then the month e.g to february (2013-03-03)
which causes a wraparound as february doesn't have 31 days.
Merge branch 'timecard' of github.com:Mayflower/PHProjekt into timecard

* 'timecard' of github.com:Mayflower/PHProjekt:
  remove unnecessary time calculation
  checkstyle
  fix calendar cache