Add / figure out where to add a feature flag for the bundler

[thisisaaronland]

This should be a Spelunker wide config that happens at start up. Chances are good it will have to go in the init method, because Flask:

https://github.com/whosonfirst/whosonfirst-www-spelunker/blob/master/www/server.py#L103-L123

For example: How do we enable this on the dev Spelunker but not prod until the prod API is live?