Enable installation in environments which require a proxy

This update is restricted to non-windows environments only. It utilizes the
collector tarball available for download via

https://collectors.sumologic.com/rest/download/tar

and replaces the bundled wrapper.conf with a template that utilizes the
system java package and the supplied proxy settings.
Merge pull request #27 from boldfield/support-proxies

Enable installation in environments which require a proxy