Calckey support

[diamondburned]

Currently, this add-on doesn't work with Calckey, probably because it hard-codes to detect an element with the query #mastodon.

Calckey uses a URL format of https://instance.org/@user, so I think the add-on can be changed to allow any URLs of that format, which will support both Calckey, Mastodon and probably a bunch more.

As for posts, Calckey uses /notes/, so this will likely have to be coded in.