date imports

The module should handle dates gracefully and uniformly. This means that all dates (the event start and end dates, the node creation date, ...) should use the same parser.

We also need to check whether dates actually work in following cases:
- timezones enabled/disabled
- ampm enabled/disabled
- non-english date formats ??

If the import of dates works as expected, we should probably remove the "event: start day", "event: start month", ... etc and only use "event: start date".

So, everyone who has some time left, please test date imports (eg with the "node: authored on") in every type of format you can imagine and with any of the possible settings.

I suppect things will break :-(