Addon deprecation system

[asportnoy]

We need some kind of system for being able to mark an addon as deprecated. There have been a couple cases already where we want to deprecate one addon in favor of another, but there is currently no way to do that. We'd add a key to the manifest like this:

{
    "deprecated": {
        "message": "Message to explain the deprecation",
        "replacement": {
            "id": "Updater info for recommending a replacement",
            "source": "store"
        }
    }
}

Both keys within are optional, and we'll allow devs to simply specify deprecated: true if they don't want to specify either.

In the updater, we'd display that the addon is deprecated along with the dev's message if specified. If a replacement is specified, we'd show a button to switch to that addon instead (show the regular install flow modal, and if the user approves the install, uninstall the existing addon). It will also show an uninstall button. No update button will be shown.

If a user tries to install a deprecated addon, we'd show a modal with the same information and buttons. Users will not be able to install deprecated addons.

In the store, we'd hide the addon from the list and from search. If the page is viewed directly, we'd display the deprecation notice with a link to the replacement if applicable. (This will be done later outside of this PR)

[ShadiestGoat]

I can take this