Toggling between maps for multiple cultural / environmental variables

Fix for #168 

Problems:
- if you search for variables where not every society has a code for each variable (e.g., search for 'Type of Slavery', and 'Ownership of Resource Locations' in Economy category), societies on the map which do NOT have a code for a variable appear black.), the societies without codes appear black on the map.  Don't know how to describe this, but I will deal with this in the next push to Github.
- What to display for society markers on society results table?  
- Still need to add a legend.