Implement the Persistent Storage Querying/Requests

[graywolf336]

Currently there are only two ways to query/request data from the persistent storage. First is via the id of the stored object and the second is if the data was associated with other objects. However, there is a need for some query support that is database agnostic (since Rocket.Chat will be moving away from Meteor in the next year or two and that opens the door for different backing database support). The idea here is to create either a query builder and/or provide classes/interfaces which will allow the database query to be built for the current database type being used.