add option to lock using nested objects using flatten object

[jupe]

e.g. resources.json:

[
{"id": "b", "hostname": "myhost", "online": true, "a": {"b": 2}}
]

requirements:

{"a.b": 2}

or via CLI: --requirements a.b=2

overlapping is not allowed - raises AssertionError if happens.

note: this returns resource object as flattened style.

Todo

• fix corners