NIP-07 (Nostr Browser Signing) Support

The HTML Uploader needs to be able to load a public key from a Chrome extension. The key will need to be stored in a global variable in the page, and displayed on the page. We need it in hex format, not npub format. Hex should be the default.

See the docs on NIP-07: https://github.com/nostr-protocol/nips/blob/master/07.md
This is a good extension to try out: https://github.com/fiatjaf/nos2x
You can find it on the Chrome store: https://chrome.google.com/webstore/detail/nos2x/kpgefcfmnafjgpblomihpgmejjdanjjp

This can then be used to prepare the `/store/` link, since it needs the pk in order to store a file to the node.