Mongo_Toolkit: enable execution of all mongo methods

We currently force the use of the `aggregate` method, which is just a small part of the mongo methods collection. Enabling methods like `count`, `replace`, `update` would simplify things.

We can take two ways:
- Have another `Query` object, that specifies the command
- Use the `Execute` method in the bhom to send custom commands.

I lean towards the latter, as it is a more advanced feature, which could compromise the database.