Adds EC crypto pattern examples in the form of unit tests.
Adds ECDiffieHellman key exchange to ICryptoProvider.

Currently only implemented for desktop.
Moves test so that known limitations aren't test failures.
Fixes build breaks in Xamarin projects.
Merge branch 'master' into EllipticCurve
Fixes some build warnings.
Fixes NRE on test teardown.
supposedly fixes a warning.
Adds all the necessary members to perform ECDsa.