Dont ignore Branding Packages Views

The 'Packages' folder in Branding was being ignored, making it hard to get files into git with the standard workflow. Now excluding it from gitignore like the 'Packages' folder in the normal Views.
Merge pull request #2166 from CumpsD/master

Don't gitignore Branding Views Packages
Support Branded Layout.cshtml

Currently you can override all views in Branding, except Layout.cshtml
because ViewStart refers to the one in the regular Views, ignoring the
one in Branding if it exists.

Added a check to see if Branding Layout exists and use that one if it's
present.
Merge pull request #2167 from CumpsD/master

Support Branded Layout.cshtml
Merge branch 'master' of https://github.com/NuGet/NuGetGallery into danliu/testfix