Add nodejs-less dependency for RHEL. Fixes #486.

Also enable "compression" of stylesheets.

Compression is used to compile the LESS stylesheets into CSS at
startup. With compression disabled, the default horizon theme does
not work because the stylesheets are served as raw LESS files.
Merge pull request #115 from DavidWittman/486-rhel-css

Merged automatically by jenkins after successful build test