Es6 node_modules are not transpiled properly

[dweiger]

If I use a es6 plugin from node_modules and import it to my own plugin the code is not transpiled to es5. That leeds to problems with ie11.
A solution would be to add 'node_modules' to gerneralIcludePaths in webpack.config.js.
I already did that in the branch 'fix-es6-node-modules'. It works for me.
@SheepFromHeaven or @jurekbarth do you see any problems with including the node modules here?
If so we should find another solution.

[janrembold]

PR #130