Expand the scope of the Toolkit

[deepakunni3]

This PR address the following,

• Add reflexive option to get_ancestors and get_descendants (Addresses #8)
• Add formatted option to return elements formatted as CURIEs
• Add support for parsing biolink names in sentence case, CamelCase, and snake_case (Addresses #9)
• Deprecate names method and add get_all_elements instead (Addresses #7)
• Add new methods to Toolkit class,
  • get_all_classes
  • get_all_slots
  • get_all_types
  • get_all_entities
  • get_all_associations
  • get_all_node_properties
  • get_all_edge_properties
• Call for slots now filters out slots that are not primary