Added RegionList the most basic IRegionGroup

 - Refactored RegionPartition to extend RegionList
 - IPartionable should really be a core concept, and renamed to IUnique for clarity.
 - Updated RegionPartitionTests to include the remove method
 - RegionPartitionTests has a more useful circle intersection test
Merge branch 'feature/region-list' into develop

 - Adds RegionList and a better designed IUnique<K> and RegionPartition
 - More tests for RegionPartition