Enable graph querying via Cypher

[codingfabi]

Cypher Query Language (CQL) is a popular query language for graph databases, namely for neo4j. We should provide a way for users to query heterogeneous graphs (or graphs in general) with CQL syntax s.t. users have to make little to no adjustments working with our graph structure. In a second step, we could not only provide query functions but cover every CRUD operation via CQL queries.

The following tasks need to be done:

• Find RegEx/general method to destructure cypher queries
• Translate destructured queries into iGraph operations
• Expose query functions via package -> users should be able to apply it to arbitrary iGraph objects.