Rearrange builds by framework, other build work

- We now have solutions and project files for .NET 2.0, 3.5, 4.0, 4.5
- .NET 4.5 has an optional build config for Entity Framework 6.
  Entity Framework 6 RC1 is included in the project via nuget, but the
  DLL references are conditional on the build config.
- .NET 2.0 uses LINQBridge for extension method and LINQ support
- Removed Visual Studio 2008 support
- Deleted monodevelop mdp/mds, mono xbuild compiles the sln/csproj
  files just fine
- NOTE: Linux/mono 3.2.1 doesn't compile .NET 2.0, LinqBridge related
Added Mono.Security for .NET 4.0

The build configurations for .NET 4.0 and 4.5 now reference
the 4.0 version of Mono.Security, while the configurations
for .NET 2.0 and 3.5 reference the 2.0 version as before.