Support advanced queries

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WebDB currently supports very basic queries at the table level:

db.mytable.get(criteria);

In this example, criteria may be:

• undefined, in which case all records are returned
• An ID, in which case either an empty array or an array with one record is returned
• A criteria object, that contains one or more criteria

The third option is most advanced, and allows us to do things like:

// Get all adults named 'Jack'
var adultsNamedJack = db.people.get({name:'Jack', age:{$gte: 18}});

What we want however, is a more advanced query mechanism that allows us to query across multiple tables and add or clauses etc. This mechanism should also allow for predefining queries and then running them by only filling in the query parameters.