Don't depend on Java

[3rd-Eden]

We should not expect our users to have java installed on their systems. The compressors that do require this functionality should only be enabled when java is detected on the users system. We can probably use https://github.com/isaacs/node-which to detect if Java is installed.

Currently the CSS compressor is the only compressor that requires Java to be installed as we already have other fallbacks for JS compression in the form of uglify.

We could add alternate CSS compressors to the stack, for example:

• https://github.com/ded/sqwish

[3rd-Eden]

See extended discussion in #53

[3rd-Eden]

Closing this as it has been resolved with the creation of crusher which uses the which library to figure out if there's Java installed on the system.