fix: events can not be dragged back to their original location

[Hapcy]

When you start dragging an event on any views it works fine, but then when you try to move it back to the original position it skips over it (you can try this in the kitchen sink).

The problem appeared when the threshold for differentiating between a drag and a click (with clumsy minor drag) has been introduced. Returning the event to the original position causes the validateDrag function to return false. To solve this I introduced a dragAlreadyMoved field which turns to true when a single dragging event has happened (meaning that it has been over the threshold at least once). When the dragAlreadyMoved flag is true we no longer care about the threshold. This had to be implemented for week view normal events and all day events and for day view events. I fixed the daily scheduler demo aswell.

I tried a few ways of solving the problem.
By saving the previous drag position and comparing to that but it required way more work in the components.
I tried using local variables (in closure scope) instead of fields for dragAlreadyMoved but it was less clear.
An alternative solution could be modifying the draggable library to call the validateDrag function with the x-y coordinates which would be used in the not snapping mode instead of the snap coordinates, but that could probably break many things because it seems really fundamental to how the draggable library works.

[codecov-io]

Codecov Report

Merging #847 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #847      +/-   ##
==========================================
+ Coverage   96.99%   97.02%   +0.03%     
==========================================
  Files          38       38              
  Lines         864      874      +10     
  Branches      118      119       +1     
==========================================
+ Hits          838      848      +10     
  Partials       26       26

Impacted Files	Coverage Δ
...r/src/modules/week/calendar-week-view.component.ts	96.1% <100%> (+0.08%)	⬆️
...rc/modules/common/calendar-drag-helper.provider.ts	100% <100%> (ø)	⬆️
...dar/src/modules/day/calendar-day-view.component.ts	95.93% <100%> (+0.13%)	⬆️

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[mattlewis92]

Apologies for the extremely late reply on this. I just had a look over this PR, and it looks absolutely perfect to me, nice job! ❤️