Allow the use of a remote manifest for download

This way, the remote manifest fetched when checking for a new version
can be passed to the download method.
This allows versionned name for the archives.
node-webkit-builder's `options.buildType` can now also be used.

Fixes: https://github.com/edjafarov/node-webkit-updater/issues/14
Escape unzip command on windows
If application path contains spaces, the cmd.exe call fails.
We need to escape properly the paths with double-quote.