Added Invoke-DscApply

Added Invoke-DscApply function to DscOperations module.
Calls the ApplyConfiguration method of MSFT_DSCLocalConfigurationManager, similar to Invoke-DscPull calling PerformRequiredConfigurationChecks.
This method will immediately reapply the current configuration, eliminating the need to "poke" multiple times with Invoke-DscPull to trigger the application of configuration. Useful for demonstrating DSC autocorrecting configuration drift.

http://msdn.microsoft.com/en-us/library/dn469245(v=vs.85).aspx