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

prepare issue branch
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