Added template date/time models
Removed debug junk
Now we can explicitly state which hierarchies to inherit from a template + tests
Renamed date/time to base_date/base_time and moved to internal dir
Minor date time model update
Load the base model; Added load_base_model flag
Don't forget to install the base model; + test
More levels
Assure level inheritance
Refactored create_dimension: unused levels and hierarchies with nonexistent levels are removed
Specify levels instead of hierarchies + added new inheritance/unused removal test