Add windows support through windows scheduled tasks

I needed to support chef-client updates on windows and I get from IRC channel for chef that in last chef summit the discussion pointed that this should be done through scheduled tasks.
I have gave it a try.
One thing I have not been able to workaround is the windows dependency on the metadata, as if you are using omnibus updater for linux, this has no sense, but I cannot find how to do conditional dependencies.

Modified the cookbook to only upgrade windows (msi installer does not support downgrade, although it could be achieved deleting current version and installing new one)