Changed aroundtime to a time window (feature #1400)

@ProfYaffle & @adamsutton I rebased and cleaned up my version of the patch as discussed in the old pull request.
I do not replicate the bug. 0 means midnight which can be 00:00 or 24:00 depending if you look at it as start or end time of the window. That is why I suppress midnight in the gui so you get ranges like:  [- 19:00] [19:00-] 19:00 - 20:00] and offcourse [20:00 - 19:00]