Test inserting Relation instances in various cases to do with role hierarchies

[alexjpwalker]

Problem to Solve

We don't currently have any Concept or Graql tests that test inserting Relation instances in the case of a role hierarchy.

Proposed Solution

These tests should be added to relation.feature in concept and insert.feature in graql/language.

An example test case is: if we do

define 
  super-rel sub relation, relates abc-role;
  sub-rel sub super-rel;

  abc sub entity, plays super-rel:abc-role:

will be able to insert abc instances playing role abc-role in sub-rel?