Tests & model-building

+ Removed test/unit
+ Added RSpec for testing
+ Wrote first unit tests based on [Location](https://github.com/codeforboston/urbanite/wiki/Location-Template-v3), [Event](https://github.com/codeforboston/urbanite/wiki/Event-Template-v3) templates
+ Wrote first sketch integration test
+ Updated `rake db:populate` to reflect model updates

Made some language changes: class `Location` is now `Venue`, as "Location" could easily refer to a point location (i.e. "geolocation"). I started thinking about "the location of a location" and realized there were Human Namespace Conflicts, so changed terminology to "the geolocation of a venue".