Merge remote-tracking branch 'origin/master' into merge-upstream

Conflicts:
	app/javascript/styles/mastodon/components.scss
	app/javascript/styles/mastodon/modal.scss

app/models/user.rb

@@ -50,8 +50,8 @@ class User < ApplicationRecord
   devise :registerable, :recoverable, :rememberable, :trackable, :validatable,
          :confirmable
 
-  belongs_to :account, inverse_of: :user, required: true
-  belongs_to :invite, counter_cache: :uses
+  belongs_to :account, inverse_of: :user
+  belongs_to :invite, counter_cache: :uses, optional: true
   accepts_nested_attributes_for :account
 
   has_many :applications, class_name: 'Doorkeeper::Application', as: :owner
@@ -223,5 +223,6 @@ class User < ApplicationRecord
   def update_statistics!
     BootstrapTimelineWorker.perform_async(account_id)
     ActivityTracker.increment('activity:accounts:local')
+    UserMailer.welcome(self).deliver_later
   end
 end