Improvements for custom periods

Based on your feedback custom periods are much more improved and now you can define more than one custom period during the one default period. For instance, during the default period of 45 minutes you can add 3 shorter lessons of 15 minutes each. When adding new custom period(s), you will be asked if appropriate cards on default periods should be moved and resized accordingly so you don't have to do it manually.

Positioning and resizing of custom cards is also improved to better supports gaps between default periods and different period intervals. When dragging a card, the card shadow will cycle through all default and custom periods beneath so you know exactly where dragged card will be dropped.

While dragging a card, the card shadow shows exact position where card will be dropped