Added powershell helpers

* this file contains a powershell and .NET blob needed for generating windows specific userdata
Merge pull request #154 from gabriel-samfira/powershell-helpers

Added powershell helpers

This file contains various helper functions that are needed to bootstrap a windows juju agent. The embeded .NET code implements a few powershell commandlets that are not part of the standard powershell library and that are needed to complete the bootstrap process.

These commandlets will be used when generating the userdata for a windows machine.