Refactor `utility_funcs.py` into smaller, more manageable modules

[Daethyra]

Reasoning

I intend to create new chatbots, for example, one with "vision," but utility_funcs.py is excruciatingly long and cumbersome.

Plan

Refactor module into smaller, more manageable modules by separating classes and functions based on categorical purpose.

• Chatbot operators:
  • RetrieveDocuments
  • set_llm
• Premade by LangChain:
  • StreamHandler
  • PrintRetrievalHandler
• Streamlit operators:
  • set_bg_url
  • set_bg_local
  • save_conversation_history