Allow configuration of drag resize minimum size

[8176135]

In the scheduler, you can drag to resize the events, however, it seems like there is a minimum size of 15 minutes.

I have increased the height of each hour segment to 18em tall, and decreased the default dragTimeStep to 5 minutes, but it seems like the minimum drag resize is still limited to 15 minutes.

The same limitation seems to apply when creating a new event.

[dioslaska]

We fixed this in 5.13.1, it takes the value from dragTimeStep for minimum event length.