Data: additional DAO queries

[lhaze]

Let's follow SQLAlchemy conventions on querying API.

Add some expected lazy queries:

• filter_by(id or ids)
• aggregate
• order_by
• annotate

... and some evaluating queries:

• slice aka [2:5]
• first (a special case of slicing)
• no-argument get (aka one) for querying unique keys that aren't id (primary key) (?)

Modification:

• get(id) should be accepting situations when object is not found (like current get_or_none)