SharpLearning.Core: Merge SharpLearning.Containers and SharpLearning.Common.Interfaces

Once #20, and #112 has been completed, the code in SharpLearning.Containers should be reduced quite a bit, and only contain a few basic types and support extension methods. For this reason it would make sense to merge this with the common interfaces assembly into a SharpLearning.Core project that holds the basic essentials for SharpLearning.