Added DataContract attributes on CacheItem class.
Added DataContract attributes on CacheItem class.

DataMember attributes with Order attribute have been added to make class compatible with protobuf-net serialization system.

moonpyk/mvcdonutcaching,gareththackeray/mvcdonutcaching,mlidbom/mvcdonutcaching,moonpyk/mvcdonutcaching,kimx/mvcdonutcaching,mlidbom/mvcdonutcaching,mlidbom/mvcdonutcaching