Refactor BlockInfo class into its own file

Refactor BlockInfo class into its own file. Was previously in
UniqueIdentifiers.cs
Refactor MatchingBlocks class into its own file

Refactor MatchingBlocks class into its own file. Was previously in
UniqueIdentifiers.cs
Refactor UniqueIdentifierPair class into its own file

Refactor UniqueIdentifierPair class into its own file. Was previously in
UniqueIdentifiers.cs