Should allow activities to start with a date

[Bytekeeper]

If an ongoing activity is started with the text like "2017-05-08_19:00:00", STT will interpret it as being an ended activity. If the date is before the start date, it will even throw an exception, when trying to enter it.

Todo:

• Introduce a separator between time and activity: "#"
• Still parse the "old" format without the "#" but silently migrate to the "#" format on the next change or for new entries at least