change filter handles to not update until mouse is released

[agurvich]

this way it is less obvious that there is latency introduced by updating the filter limits.

[agurvich]

@ageller this is super noticeable for undecimated datasets. not so bad with the ones we're hosting online but when I was pushing the memory limits it was really hard to filter stuff.

[ageller]

Hmm. I'll have to try this on my end with a huge data set. (Haven't done so in a while.) One option could be make this conditional: if the number of particles is very high, then you go with this method, otherwise use the usual method.