SOS - Observed Properties added in metadata.py, Exception logging in server.py

Suggested changes for parse_sos observed properties begin here: https://github.com/DanRamage/pycsw/blob/master/pycsw/metadata.py#L707
This adds the observation name to the keywords database field. It takes into account if the entry is a URI or URN type field and strips away everything except the observation name.

server.py logging added here: https://github.com/DanRamage/pycsw/blob/master/pycsw/metadata.py#L707
To help track down the actual server error, the exception logging to file is added.


Can we make a bit more generic, like:
```python
if obs.lower().startswith(('urn:', 'x-urn:')):
```