Support project specific project and gazetteer structure

[davidorme]

At the moment, the gazetteer and project resources have a fixed structure because of the need to populate a table in safedata_server. The table definition in the web application has a fixed list of fields.

This can either be fixed by dynamically building the table definition over on the server or by coming up with a simple configuration option here that provides the table structure. That last one seems preferable because you don't really want the structure of those tables to change - it should be defined once and then future resource updates can add rows but not change fields.

It might be easiest simply to describe how to edit the safedata_server resources.py model. At least initially - some kind of tool would be good but this is such a low frequency event - make this part of the guide in #104 .