Added BouncyCastle.sln and csproj which are in VS2010 format

Target .NET 2.0 instead of 1.1 since no one uses 1.1 anymore.

Also don't compile the unit tests & data into the crypto assembly.

I wasn't able to migrate the unit tests to VS2010 mostly because I haven't figured out how to get the unit tests migrated over to a newer NUnit release (I've got 2.4.8 installed, but I think they are up to at least 2.6.x).

Not sure if this pull request is valuable at all, but figured I'd submit anyway in case it is helpful.