Replaceable event notifications & subscribed notifications for non-mentions

[v0l]

Made quite a few changes here..

1. Changed notification settings to use a comma separated list of kind numbers instead of boolean flags.
   This is still backwards compatible as the API calls are the same, you can use the boolean flags to set the kind number.
2. Added a new concept called notify_keys which allows users to subscribe to notifications on when another pubkey posts an event (Live Stream / Article etc)
   This required a change to the notifications table to create a distinct key for replaceable events so that we only see a notification once (When its first published)

This PR includes all the changes i also made for FCM so it depends on #19

Direct compare: https://github.com/damus-io/notepush/compare/cbe9a65ccfaed67bb8cc6d9816cff04eeda2cb7c..44aade5de70219af238086df1783094bf1db3b2a

[jb55]

oops just saw this! reviewing

[v0l]

Feel free not to merge this, i ended up making a bunch of changes that you might not want