Rename index.css and require.js with md5 hash

- removes obsolete "cache buster" setting
- replaces hardcoded require.js and index.css filenames in settings
files for non-dev build processes with variables.
- `release` and `couchapp_deploy` tasks now rename those two files to
include their hashes, and reference them in the generated index.html
file
Nice, thanks @robertkowalski! Will do.