Add missing .gitattributes, and applies standard .gitignore file.

The .gitignore file we had before was a small subset of the default .gitignore file applied by VS (which comes from github). So I replaced ours with the one from VS. I also added a couple more .gitignore files to cover the packages folders in sub-directories. I could have modified the original root .gitignore file to cover this, but I felt keeping the file at the standard one will make upgrading it to newer standards easier. It also helps keep the file's concerns localized.