Modify cosine similarity based graph extraction to take into account guiding terms

[bsantan]

For all input types, add optional guiding term option to select for paths more similar to given concept using cosine similarity search

1. Support --guiding-term boolean in command line (inputs.py)
2. Add required file to input directory for all input types if boolean is true (guiding_term.csv) (inputs.py)
3. Perform indexing for guiding term (check if guiding_term_label.csv exists first) (assign_nodes.py)
4. Output guiding term labels file (guiding_term_label.csv) to output directory (assign_nodes.py)
5. Create new subgraph_prioritized_path_cs_guiding_term function using guiding term rather than target node (create_subgraph.py)