Add support for nuget pack -Verbosity and -Properties switches

As of NuGet 2.0, the NuGet.exe Pack command-line supports a few new switches and some are deprecated.  I'm adding support for the Verbosity (which replaced Verbose) and Properties switches.  Properties is especially handy for specifying a build configuration.

The **MSBuild.Community.Tasks.Tests** project didn't have tests for the `MSBuild.Community.Tasks.Nuget` namespace, so my changes didn't involve any tests either.  With more time, perhaps I could add some tests.  However, these changes were manually tested against another project of mine.