Finish up implementing adjacency list based graph class

[handlessdude]

Make sure class include:

• [x] initialization by json import
• [ ] initialization by taking adjacency list as parameter (in hash presentation)
• [x] vertices array getter
• [x] edges array getter
• [ ] inserting a new vertex to existing graph
• [ ] inserting a new edge to existing graph
• [ ] output to standard output stream (useful for graph mutation debug)
• [ ] output to json file (useful for graph mutation debug)
• [ ] necessary tests
• [ ] necessary docs

[selfmadekirich]

take it