Entity Framework  6

In EF6 everything from `System.Data.Entity.dll` was moved to `EntityFramework.dll` and namespaces were also changed.

I inserted the new namespaces surrounded with `#if ENTITIES6` so that nothing changes if you are using a previous version. Since I also had to remove a reference to `System.Data.Entity` I created a new project `NpgsqlEF6` which targets v4.5 and defines `ENTITIES6` and has this reference removed.

If you are like me and want to use the new Entity Framework 6 now, you can use the `NpgsqlEF6` project and for everyone else nothing changes.