implement a more user-friendly interface

We should re-implement a friendlier user interface that allows:
- Drag and drop, or file upload, approach in importing documents
- Focusing on letting the documents answer the questions
- Being able to jump to the corresponding position of the imported document
- Perhaps letting the LLM to rephrase the chunks in response to the user's query?
- Perhaps displaying fewer results upfront and allowing for quick switch. This is intending to prevent the user from being overwhelmed.