HTML: Compile Scrubbers on boot

This makes it possible to configure their behavior on OTP releases.

lib/pleroma/application.ex

@@ -30,6 +30,7 @@ defmodule Pleroma.Application do
   # See http://elixir-lang.org/docs/stable/elixir/Application.html
   # for more information on OTP Applications
   def start(_type, _args) do
+    Pleroma.HTML.compile_scrubbers()
     Pleroma.Config.DeprecationWarnings.warn()
     setup_instrumenters()