CLI hql filter

As discussed in https://github.com/openmicroscopy/openmicroscopy/pull/3119#issuecomment-61489143, `False` values are currently systematically filtered out of the `hql` output. 

This PR refactors the `HqlControl.filter`  criteria by:
- adding a top-level keys blacklist list (`_id`, `_loaded`)
- filtering out all `_xxxLoaded` keys 
- preserving the test for empty values using `if not` but explicitly allowing `0` and `False` values

Corresponding unit tests are added and should be passing in Travis. Additionally, this PR should be tested against a server by checking the output of queries on basic objects:

```
bin/omero hql 'select e from Experimenter e'
bin/omero hql 'select i from Image i'
...
```