Update worker bundles to IIFEs

[benkeen]

This requires a bit more investigation and experimentation, but so far it appears to work fine.

The current rollup bundling process for the web worker bundles is pretty lightweight: it doesn't accommodate proper imports and won't work for the Bitcoin plugin which has external dependencies. Also when we move this app to run as a a server app we'll need to extract the generation code from the workers themselves - since they won't run on the server and are kinda klutzy in that context. So again we'll need to generate proper bundles, using the web worker wrapper as the target in each place.

• check bundle sizes
• check all DTs and ETs

[benkeen]

Don't think this is now needed. We've extracted the generation code from the worker code and there's basically just boilerplate left.