Move hierarchy out of spec and into lib
Hierarchies must have a name, and don't know if they're roots
Fix structure_spec so it can run indpendently of others

It was relying on the fact that one of the other tests
accidentally defined all of the constants on Object
Add specs for integrating hierarchies into Structure
Reorganize structure_spec to be more cohesive
Add specs for integrating the hierarchies into the timeline
Shorthand rake tasks that I keep mistyping
Hierarchy is initialized with a hash of attributes instead of ordinals
If tags are not provided, they default to empty array