Add withConcern method and apply it for Save

refs #94
Apply withConcern for Remove

refs #94
Apply withConcern for Update

refs #94
Allow VisibilityChecker configuration

refs #89
Rename StandardModifier to PropertyModifier

refs #89
Polish VisibilitChevcker test
Apply withConcern for Insert

refs #94
Replace LazyWriteableDBObject by LazyDBObject
Merge pull request #100 from bguerout/feature/writeConcern

Add MongoCollection.withConcern(..).operation(..)
Merge pull request #101 from bguerout/feature/visibility-checker

Allow VisibilityChecker configuration
Merge update.with(pojo)