Fix broken API endpoints and logic errors and added dependencies

[Domenez-dev]

The script was broken because the Pushshift API is offline. I have:

• Switched to the official Reddit JSON API so the script fetches data again.
• Fixed the graph generation logic to prevent crashes when a user has no activity during specific hours or days.
• Added a check for the missing all-locations.txt file.
• Added a custom User-Agent to avoid being blocked by Reddit.
• Added requirements.txt file to easily install dependencies