global: Zenodo test records

* Updates INSTALL.rst with information about database pouplation.

* Adds xml with test records.

Signed-off-by: Adrian Pawel Baran <adrian.pawel.baran@cern.ch>
Could you set this in ``zenodo/config.py`` instead and using ``pkg_resources`` to find the demo records (like in the demosite populate command).

```python
BASE_DEMOSITE_RECODRS_FIXTURE = [pkg_resources....]
```

Also, you will likely need to add ``demo_zenodo_record_marc_data.xml`` to the MANIFEST.

Lastly, to test the record loading, you should update ``.travis.yml`` with:

```
- "inveniomanage demosite populate || echo ':('"
```