fix #1272 - add support for ref folder in package installation

[sbwalker]

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[sbwalker]

This PR contains a variety of fixes/improvements:

• fix Nuspec to include 'refs' #1272 - add support for ref folder in package installation
• consolidate package installation to wwwroot/Packages folder ( Modules and Themes folders are still supported for backward compatibility )
• installation manifest now stored in Packages folder using packagename.log file
• added UnnstallPackage() method to consolidate logic for processing manifest file
• fixed issue in module and theme uninstall where the item was still displayed in the grid after uninstall
• fixed issue in module uninstall which would sometimes throw an error "Database operation expected to affect 1 row(s) but actually affected 0 row(s)"