Move to webpack

[fcaps]

the current status is we are running grunt for a couple of tasks and webpack for some other.
in favor of "well-known" webpack we should move all what's left to webpack.

[] scss -> css
[] nodemon -> devserver
[] change docker prod/dev
[] remove grunt and deps
[] remove exceptions from .npmcheckrc

there are surely some issues on the way, but someone has to start it.
would be perfect if we also combine it with #500