Low Default PBKDF2 Iterations

See here: https://github.com/JaCraig/Craig-s-Utility-Library/blob/master/Utilities/IO/Encryption/BaseClasses/SymmetricBase.cs#L140

This code sets the default iteration count to a value well below the recommended values - see here for some well known values. The default value, if one is supplied, should be in the thousands - not the two it's currnetly set to.

The default value is set so low that it provides practically no additional value.