set up general callback from yearslider for enable/disable
make object deep copy calls more readable
cache the maxSingleYearQuantity for the current filters

So that we can use it to have a consistent max quantity when hitting
"play years".
Allow the arrows max quantity to be set when calling drawRouteCol..()
Get the maxSingleYearQuantity for either plain arrows or flowmap
Use the maxSingleYearQuantity when drawing data for a single year