ChatGPT Export as Text per tnndvd

Adds download buttons to save ChatGPT replies or full conversations as plain text.
Also present a download button for codeblocks: the downloaded file in this case is not a .txt but has the relevant extension (e.g. .js for javascript or .sh for bash).

Disclaimer:
This project is not affiliated with OpenAI, ChatGPT, or any related service. It simply adds functionality to pages that the user is already viewing in their browser.