Catch exceptions in js minifier and don't re-minify single files

[jehhynes]

1. Was running into an internal error in NUglify minifying a bundle which included signalr.js (cdnjs package "microsoft-signalr@6.0.1"). Strangely, in this package, signalr.js and signalr.min.js are both minified. Regardless, we should not just die when NUglify has internal errors. Instead, gracefully handle the exception and use the unminified version instead.
2. Looks like there is code in place to skip reminifying bundles that are already minified, but not single files when bundling is disabled, so I added a check for .min.js, .min.css, .min.html in the corresponding minifier classes (in addition to the ".min" check)

[madskristensen]

Thanks