Created MongoDB template.

Hi Arjen,

I created wrapper over Spring Data MongoDB template together with some useful implicit conversions for template callbacks.

I created the tests to cover the most important template methods. I will submit the full test coverage in the near future. I use excellent EmbedMongo library [1] for testing. EmbedMongo is available in Maven central.

I would really appreciating peer review and possible merge of this feature. I would like to include it in a bleeding-edge project for a customer of mine. Early adoption FTW :) .

Cheers.

[1] https://github.com/flapdoodle-oss/embedmongo.flapdoodle.de