Separate PuSH subscriptions from following, add mastodon:push:refresh task,

respect hub.lease_seconds (fix #46)

app/services/subscribe_service.rb

@@ -0,0 +1,20 @@
+class SubscribeService < BaseService
+  def call(account)
+    account.secret       = SecureRandom.hex
+    account.verify_token = SecureRandom.hex
+
+    subscription = account.subscription(api_subscription_url(account.id))
+    response = subscription.subscribe
+
+    unless response.successful?
+      account.secret       = ''
+      account.verify_token = ''
+
+      Rails.logger.debug "PuSH subscription request for #{account.acct} failed: #{response.message}"
+    end
+
+    account.save!
+  rescue HTTP::Error, OpenSSL::SSL::SSLError
+    Rails.logger.debug "PuSH subscription request for #{account.acct} could not be made due to HTTP or SSL error"
+  end
+end