Fix #61 - Add list of blocked users to the UI; clean up failed push notifications API

Try to fix Travis CI setup

db/migrate/20170205175257_remove_devices.rb

@@ -0,0 +1,5 @@
+class RemoveDevices < ActiveRecord::Migration[5.0]
+  def change
+    drop_table :devices
+  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: 20170129000348) do
+ActiveRecord::Schema.define(version: 20170205175257) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -54,15 +54,6 @@ ActiveRecord::Schema.define(version: 20170129000348) do
     t.index ["account_id", "target_account_id"], name: "index_blocks_on_account_id_and_target_account_id", unique: true, using: :btree
   end
 
-  create_table "devices", force: :cascade do |t|
-    t.integer  "account_id",                   null: false
-    t.string   "registration_id", default: "", null: false
-    t.datetime "created_at",                   null: false
-    t.datetime "updated_at",                   null: false
-    t.index ["account_id"], name: "index_devices_on_account_id", using: :btree
-    t.index ["registration_id"], name: "index_devices_on_registration_id", using: :btree
-  end
-
   create_table "domain_blocks", force: :cascade do |t|
     t.string   "domain",       default: "", null: false
     t.datetime "created_at",                null: false