[TEST] Added ability to test apis that don't return json

The last response body gets now always stashed in the REST tests and can be retrieved via `$body`. This implies that not only expected values can be retrieved from the stashed values, but actual values as well.
Added support for regular expressions to `match` assertion, using `Pattern.COMMENTS` flag for better readability through new custom hamcrest matcher (adopted in do section as well).

Added also example tests for cat count api