Use the newer AppDeployCmd when available
The old XapDeployCmd could raise "Error: The parameter is incorrect." with project files that were opened with more recent versions of Visual Studio.
This change looks for the Windows Phone SDK 8.1 AppDeployCmd before falling back to the WP SDK 8.0 XapDeployCmd.
Merge remote-tracking branch 'hartwig-cordova/feature/appdeploy-wpsdk8.1'
CB-8060 Updated AppDeployCmd lookup code

github: close #67