Update VariantTrack on any prop/state change.
Update VariantTrack on any prop/state change.

Previously it ignored height/width changes.
Fixes #253

hammerlab/pileup.js,piotr-gawron/pileup.js,snaheth/pileup.js,hammerlab/pileup.js,piotr-gawron/pileup.js,snaheth/pileup.js,hammerlab/pileup.js,hammerlab/pileup.js,snaheth/pileup.js,piotr-gawron/pileup.js,piotr-gawron/pileup.js,snaheth/pileup.js