Fixes for NuGet Packager

Packager actually writes the title and iconUrl metadata now.
Modified required metadata properties to match NuGet spec.
Added property to allow custom specification of the location of
NuGet.exe command line tool.
Continued Fixes for NuGet Packager

Added metadata properties releaseNotes, summary, language, and
copyright. Should now support all available metadata specified in the
Nuspec Reference.
Merge pull request #13 from baerbradford/master

Fixes for NuGet Packager