Watch static directory during --watch.

[Zegnat]

I am working on #60 and needed a permission change. Then spent 10 minutes furiously reloading the extension and wondering why it wasn’t working: files from the static folder aren’t watched and moved to the dist folder by the build process.

I don’t know enough about this build system setup to know if it can be updated to watch the static folder too. Input welcome! Right now I need to ^C and start webpack anew, which is a lot slower than the --watch process.