changed the logic of how derStandard puzzle ids are matched to dates

Instead of trying to match the actual release date of puzzles to their IDs (which was complex, error-prone and slow), we now assume daily releases (for easy conversion from date to id) with a freely configurable starting id for june 1 2014.

This simplifies this thing a LOT and gives us access to a large back-catalogue of puzzles; the latter is useful because actual puzzles aren't released daily (due to sundays/holidays) so we will catch up over time and eventually run out of puzzles. But that shall be handeled at a later date.

This also removes the neccessity for a cache file for puzzle metadata.