Optimize build

[it-vegard]

The build time is too slow for the size of the project. Should look into ways of optimizing it, like using parallell npm processes, splitting up the webpack build, only optimizing file sizes for build (not watch) tasks, etc.

At the moment, gradle uses node tasks, while we can call the gradle build using npm as well. Should probably save some time using things natively, perhaps integrating it in the webpack build?

Suggestions are welcome!