new features for MoBEM Maker

[elisabeth-chen]

Liz:

• [x] finish writing filter code
• [x] add matrix creation function
• [x] make filter code into class
• [x] add drug download + conversion module
• [ ] integrate fetch_gdsc_data, annotate_gene and filter_genes into clear work flow
• [x] make flowchart
• [ ] discuss with Mathew to decide final naming convention and required user input
• [x] create documentation + tutorial

Thomas:

• [x] add tests
• [ ] use stringiu to read excel into memory

[cokelaer]

changes planned for v0.16.1

• [ ] instead of filling NA with "", we drop the rows. In any case, we do want to end up with genes or tissues that are unknown and set to empty strings.
• [ ] Not sure what plot_alterations_per_cellline is suppose to do ?