Ambiguous reference to Signal and Tuple

[dharmatech]

The build fails with this error:

Error   1   'ISet' is an ambiguous reference between 'System.Collections.Generic.ISet<MathNet.Symbolics.Signal>' and 'MathNet.Numerics.ISet<MathNet.Symbolics.Signal>'
C:\Users\dharmatech\Documents\mathnet-yttrium - d\src\app\MathNet.Yttrium\Contracts\Containers\ISignalSet.cs    29  35
Yttrium.Contracts

I was able to resolve this by fully qualifying MathNet.Numerics.ISet.

There were many similar errors for Tuple as it's in both System and MathNet.Numerics. These were resolved in the same way.

I'll be happy to supply a patch for these if this is the correct way to fix these.