DATAMONGO-812 - Add support for $push $each since $pushAll is deprecated.

$pushAll has been deprecated in MongoDB 2.4. Instead of calling pushAll one can use push in combination with each. The abstraction for pushAll will remain in code for now but may be removed in a subsequent version.

Original pull request: #112.
DATAMONGO-812 - Polishing.

Changed convertToMongoType(…) to forward type hints to recursive calls to make sure type information is written if a TypeInformation was provided initially. Make sure that UpdateMapper hands in an initial type hint to the converter to make sure type information gets written.

Changed the signature of QueryMapper.getMappedObjectForField(…) to allow customizing the entire entry being added to the result. This is in preparation of more advanced mappings that might have to customize the mapped key.

Fixed newly introduced test cases in MongoTemplateTests.

Original pull request: #112.