Some users encoutered a bug where WebUI in browser show a white screen,
which indicates a problem with loading javascript files. The problem was
due to closure minifying failure leaving a zero-length deluge-all.js
file which broke the usual fallback mechanism to debug files.
* Fixed usage of ES6 const declaration breaking closure minifying.
* Cleanup minified files upon errors so no zero length files left
* Replaced broken and unmaintained slimit with rjsmin.
* Fixed unable to set dev or debug query args due to request args
requiring bytes.
a03e649da6