Allow event to be moved (and duration changed) while still in "edit" mode, like Google Calendar

[connecteev]

I believe this feature will take dayspan-vuetify to another level.

https://clickermonkey.github.io/dayspan-vuetify/example/

Go to the "week" view (same thing should apply to other views like "Month" though)
Click on the calendar to add an event. A date and time gets selected based on where you clicked, and a modal is shown to create the event.

However, you cannot:

1. Drag the event to move the day/time (like you can on Google Calendar)
2. Drag the bottom of the event placeholder to change the duration (like you can on Google Calendar)
   For issue 1, you have to click out and click again, but you may not be great at clicking precisely at the right place...especially if the calendar is crowded.
   For issue 2, there's no way to do this until you create and then edit the event.
   I think both of these problems can be solved if we do how Google calendar does it.

See https://calendar.google.com/calendar/r/week/2019/4/6 for how this works.