Support Users Directly Uploading Profile Pictures.

* Adds a `picture` attribute to `User`.
* Preserves Gravatar as a fallback option.
* Now, you should use `user.profile_picturer` instead of `gravatar_url`
* TODO: Ensure `profile_picture` handles sizing right for uploaded images.

db/migrate/20200715034647_add_picture_to_users.rb

@@ -0,0 +1,5 @@
+class AddPictureToUsers < ActiveRecord::Migration[5.2]
+  def change
+    add_column :users, :picture, :string
+  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: 2020_07_15_001812) do
+ActiveRecord::Schema.define(version: 2020_07_15_034647) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -591,6 +591,7 @@ ActiveRecord::Schema.define(version: 2020_07_15_001812) do
     t.boolean "is_admin", default: false
     t.string "username"
     t.boolean "is_disabled", default: false
+    t.string "picture"
     t.index ["confirmation_token"], name: "index_users_on_confirmation_token", unique: true
     t.index ["email"], name: "index_users_on_email", unique: true
     t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true