Removed ConnectionScope from ISessionBase

Tidies up the Transaction class as the Connection opening and closing is
now performed by SessionBase alone rather than being split between them.
Use It.IsNotNull<> over It.IsAny<>

It.IsAny will pass if the value passed is null, using It.IsNotNull will
fail which allows us to prove that we have passed non null arguments
MsSqlDbDriver should also override Combine(SqlQuery, SqlQuery)
Closes #296
The else doesn't actually make any difference

If we match an if, we throw an exception. If we don't then we want to
evaluate the next if regardless.
Deleted unneeded files
Closes #297
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Updated NuGet.exe