Added theme overlay support. Updated zip handling in user-installable packages.
Digest:
- server-node: Updated user-installable package handling
- build: Updated help
- build: Support for theme overlays
- build: Separated sound theme build from main
- misc: Updated bin/add-user.js
- misc: Updated Grunt tests
- misc: Changed from 'unzip' to 'unzip-stream' library
- misc: Updated package.json dependencies