Progress updated documentation

[ECharria]

The docs folder was modified as:

1. mkdocs.yml strucutre was changed to include the correct structure of the documentation tabs
2. All figures were transferred into docs/docs/figures
3. Now the docs folder includes the api, examples, figures, guide, and home folders as well as the index.md file
4. The api and examples folders have not been changed
5. the guide folder now includes:
   • MS2LDA_Command_Line.md (CLI guide)
   • MS2LDAViz_App.md (Viz app guide)
   • overview.md
6. The home folder now includes:
   • behind_MS2LDA.md
   • quick_start.md
7. The global index.md file was modified to include all changes