Code splitting support

[yyx990803]

Theoretically we should be able to support async components imported by the tested component when using mocha-webpack with the following config:

• target: 'node' for webpack
• optimizeSSR: false for vue-loader

But there are still some issues right now that prevents it from working. Need to investigate a bit further.

Most of the time splitting is done at route level so this is not a high priority concern, but would be nice to figure it out down the road.

[JessicaSachs]

Hey @yyx990803, seemingly there is a working test that exercises dynamically imported components. (link) Am I missing something?