DATAMONGO-807 - findAndModify does not retain Class information

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DATAMONGO-807 - findAndModify does not retain Class information.

Using findAndUpdate did not retain _class information when used to update a whole nested type instead of single fields within the type. We now use the updateMapper in doFindAndModify for the update operation to make sure to retain the type information - previously we just used the queryMapper.

Original pull request: #110