Add query selectors and sort API

[ecarriou]

Add some basic query selectors, example:

• runtime.require('db').collections().Jedi.find({'name', {'$eq': 'name'}})
• runtime.require('db').collections().Jedi.find({'age', {'$gt': 30}})
• runtime.require('db').collections().Jedi.find({'name', {'$in': ['Luke', 'Dark Vador']}})

Add basic sort API:

• runtime.require('db').collections().Jedi.find().sort({'name': 1})