Allow configuring default resolution for bigwig files

[cmdcolin]

Feature request

requested by https://github.com/carolyncaron to add default configured resolution

this could be done one of two ways

1. specifically add one new config to the linearwiggledisplay (or bigwigadapter?) to solve this
2. allow configuring an entire default state initialSnapshot, potentially across all track types, to enable stuff like this more widely

Footnote

Currently resolutions in bigwigs are actually a "multiplier" that we adjust the zoom level by to drop into a different hard coded zoom level in the bigwig files

This generally works ok

we could alternatively let people pick the precise resolution bins but these are hard to predict up front and wouldn't really work well for config probably.

[cmdcolin]

fixed by #4619