added new typeconverter GuidConverter
implemented usage of the new GuidConverter
added unittests for guidconverter SerializeGuid and DeserializeGuid
uncommented assertion check
changed serialization format of guids

- 9462790d5c44468985425e2dd38ebd98 will now be 9462790D-5C44-4689-8542-5E2DD38EBD98
adapted unittests to the new guid format
Merge pull request #112 from 1and1-webhosting-infrastructure/feat-guid-support

Support of System.Guid serialization