Make overriding the location of .targets/assemblies easier

[sayedihashimi]

If you want to build using a different set of .targets then today you need to specify the following parameters on the command line

msbuild .\WebApplication1.csproj /p:VisualStudioVersion=11.0 /p:DeployOnBuild=true /p:PublishProfile=ToPkg 
    /p:PackageWebTargetsPath='C:\data\my-code\package-web\src\Nuget\Sedodream.Package.targets' 
    /p:SlowCheetahTransformXmlTaskPath='C:\data\my-code\package-web\src\lib\SlowCheetah.Xdt.1.1.1\lib\SlowCheetah.Xdt.dll' 
    /p:SlowCheetahTransformXmlExePath='C:\data\my-code\package-web\src\lib\SlowCheetah.Xdt.1.1.1\lib\SlowCheetah.Xdt.exe' 
    /p:SlowCheetahXdtAssemblyPath='C:\data\my-code\package-web\src\lib\Microsoft.Web.Xdt.1.0.0-alpha\lib\net40\Microsoft.Web.XmlTransform.dll'

We should be able to override this with a single property not multiple as required here.