remove unused files, reflect changes in documentation

[stefansc1]

Get confirmation for following files:

• [x] optimization/functions (empty directory)
• [ ] framework/functions/calculate_external_costs (function calculate_costs_for_external_components) - Nooo
• [x] framework/functions/plot_interactive_results (function plot_interactive_smooth_results)

• [x] framework/functions/save_important_parameters

• [x] Is seaborn still required (only used in save_important_parameters)?

  • [x] If so, can this be changed to pyplot?

• [x] remove deleted files from documentation