Add harpoon component

[NickCondron]

Creates a component that works with harpoon (https://github.com/ThePrimeagen/harpoon) showing the current file's harpoon index (if it exists). Right now this is a proof of concept. I want to hear your opinion on adding components for third-party plugins. This functionality couldn't be added as an extension because it doesn't involve a separate file type.

Todo:

• cache indicies
• use hook off icon, add colors, etc
• documentation