Refactor the use of our own MD5 Implementation

There are subsequent pull requests that expect the Md5CryptographicService to exit. Rather than rename that file (from a P/R), a better approach is to separate the MD5 implementation into it's own
file, then restore the MD5Service and just have it change the algorithm it uses.

product/roundhouse.tests/cryptography/CryptographicServiceSpecs.cs

@@ -38,7 +38,7 @@ public class when_using_MD5_to_do_cryptography
             [SetUp]
             public void we_set_the_context()
             {
-                md5_crypto = new ManagedMD5CryptographicService();
+                md5_crypto = new MD5CryptographicService();
             }
 
             [Test]
@@ -62,7 +62,7 @@ public class when_using_an_unofficial_md5_implementation
 
             private ThreadLocal<Random> _rng;
             private ThreadLocal<byte[]> _bytes = new ThreadLocal<byte[]>(() => new byte[max_len]);
-            private ThreadLocal<ManagedMD5CryptographicService.MD5> _unofficial = new ThreadLocal<ManagedMD5CryptographicService.MD5>(() => new ManagedMD5CryptographicService.MD5());
+            private ThreadLocal<LocalMD5Implementation> _unofficial = new ThreadLocal<LocalMD5Implementation>(() => new LocalMD5Implementation());
             private ThreadLocal<MD5> _official = new ThreadLocal<MD5>(() => MD5.Create());
 
             [SetUp]