Support for "running" callback argument.

[olegrimko-etg]

Hi!

Recently I've had a case with disabling controls while callback is running and native Dash solution using running= would be very handy. But it is not supported in Django wrapper in latest version.

This patch is just quick partial implementation of one internal field support, which are supported in referenced Dash version, but ignored in this lib.

May be someone is already working in it? Otherwise I could prepare normal upgrade PR at least for callback kwargs

long = _kwargs.get("long")
manager = _kwargs.get("manager")
running = _kwargs.get("running")
on_error = _kwargs.get("on_error") 

It looks like some internal methods were copied from Dash. Possibly it just need upgrade, but I didn't tested it all yet, only running option.