👷 Add makefile target to display ontology statistics

[ccamel]

Idea

Add a new target to the Makefile that will display several statistics about the ontology. This target will be useful to get a quick overview of the ontology and to monitor its growth over time.

Todo

Add a new target in the Makefile called stat that will generate statistics such as:

• Total number of triplets
• Number of classes
• Number of properties
• Number of instances
• Number of namespaces

This information will be outputed to the stdout in a user-friendly way, making it easy to read and understand.