introduce a basic mongo repot for crud

[lucagiove]

[lucagiove]

@gtoselli I'm wondering whether is better to have repo with a characteristics instead of purpose.
For instance:

• RepoWithOptimistcLock
• RepoWithSoftDelete
• RepoWithOutbox

Instead of AggregateRepo QueryRepo BasicRepo etc.. I'm not convinced about what I'm writing..
Or maybe we could then define AggregateRepo as an extension of RepoWith, but if someone wants to build it's own repo can compose it?