Introduce contains_only condition

We want to be able to say whether or not a pg array was containing
**only** a subset of another one.

This is supported only on PostgreSQL at the moment, and it requires
the `intarray` extension.
Skip failing analyzer_test specs

These specs never worked. It will require a certain amount of time
to understand the whole logic.
This is a development tool and can be done separately.

```bash
NoMethodError: undefined method `shift' for :permissions:Symbol
    /vagrant/lib/declarative_authorization/development_support/analyzer.rb:212:in `process_call'
```
Maintenance for 3.2+ only
Setup PostgreSQL for testing purposes
Add spec coverage for contains_only
Add specific if for contains_only
Merge pull request #8 from cfabianski/feature-add-include-only

Feature add include only