Change "addons.mozilla.org" in reviewer email templates to "addons.thunderbird.net"

[Sancus]

There's a bunch of email templates in src/olympia/reviewers/templates/reviewers/emails that have the wrong site URL hard coded, this is an easy fix and should cause very few if any conflicts with future patches, so might as well do it.

[kewisch]

bonus points for changing the hardcoded host to a variable and also pushing that patch upstream :)

[Sancus]

If they'll take the patch I'll definitely do it that way.

[holle]

Also submitting addon to https://addons.thunderbird.net/ which leads to a validation error and opening a ticket from the embedded short link also leads to the https://github.com/mozilla/addons/issues/... form instead of this project

[Sancus]

This was fixed a long time ago by da6fdef