Ability to specify certain delay before drag start to be captured

[troggy]

I want to prevent accidental drags which may happen with fast clicks on the items. Using 'distance' option isn't helping: my tree items are small enough and with bigger 'distance' values behavior starts seem confusing.

What might help is the 'delay' option similar to one from JqueryUI (here is the demo: http://jqueryui.com/resources/demos/draggable/delay-start.html).

[johnny]

pull request merged