Improve chain picker performance

[jmrossy]

Problem

The chain picker in the widgets lib works okay but lags a bit on slow machines or slow connections, mostly because we have so many chains and that's a lot of logo imgs to load.

Solution

Use a virtualized list to lighten the load or find some other way to improve the performance.

Note to future developer: If you reach for a 3rd party lib to handle the virualization, please make sure it's lightweight, reputable, and well maintained