Switch to static URIs, new URI format in both protocols for new statuses (#4815)

* Decouple Status#local? from uri being nil

* Replace on-the-fly URI generation with stored URIs

- Generate URI in after_save hook for local statuses
- Use static value in TagManager when available, fallback to tag format
- Make TagManager use ActivityPub::TagManager to understand new format
- Adjust tests

* Use other heuristic for locality of old statuses, do not perform long query

* Exclude tombstone stream entries from Atom feed

* Prevent nil statuses from landing in Pubsubhubbub::DistributionWorker

* Fix URI not being saved (#4818)

* Add more specs for Status

* Save generated uri immediately

and also fix method order to minimize diff.

* Fix alternate HTML URL in Atom

* Fix tests

* Remove not-null constraint from statuses migration to speed it up

db/migrate/20170905165803_add_local_to_statuses.rb

@@ -0,0 +1,5 @@
+class AddLocalToStatuses < ActiveRecord::Migration[5.1]
+  def change
+    add_column :statuses, :local, :boolean, null: true, default: false
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170905044538) do
+ActiveRecord::Schema.define(version: 20170905165803) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -315,6 +315,7 @@ ActiveRecord::Schema.define(version: 20170905044538) do
     t.integer "reblogs_count", default: 0, null: false
     t.string "language"
     t.bigint "conversation_id"
+    t.boolean "local", default: false
     t.index ["account_id", "id"], name: "index_statuses_on_account_id_id"
     t.index ["conversation_id"], name: "index_statuses_on_conversation_id"
     t.index ["in_reply_to_id"], name: "index_statuses_on_in_reply_to_id"