Changes to dashboard statistics. Fixes #1617

Compute Resource menu was shown only if libvirt bindings were installed

fixes #1609 - REST API calls /hosts/:id/puppetclasses fails for hosts with same class assigned directly and through host group

refs #1503, ensures that puppet proxy is not required if you are not provisioning

fixes #1600 - records are deleted even though host is not Managed

fixes #1566 - Puppet CA set incorrectly when only one proxy is defined

fixes #1254 - initial support to pxeboot windows

removed puppet from Gem file requirement

this commit also tries to simplify the way we use bundler, in future commits,
we should add more logic of which gems to load based on configration file.

make sure foreman doesnt blow up when running without libvirt / virt gems

ensure facts importer works correctly also when importing from a report / rake task