users: add /profile page (fix #4151).

* Add /profile, /profile.json endpoints.
* Make "My Account" link to /profile.
* Add 'User ID' field to profile page.

app/controllers/users_controller.rb

@@ -36,10 +36,21 @@ class UsersController < ApplicationController
 
   def show
     @user = User.find(params[:id])
-    @presenter = UserPresenter.new(@user)
     respond_with(@user, methods: @user.full_attributes)
   end
 
+  def profile
+    @user = CurrentUser.user
+
+    if @user.is_member?
+      respond_with(@user, methods: @user.full_attributes, template: "users/show")
+    elsif request.format.html?
+      redirect_to new_session_path
+    else
+      raise ActiveRecord::RecordNotFound
+    end
+  end
+
   def create
     @user = User.new(user_params(:create))
     if !Danbooru.config.enable_recaptcha? || verify_recaptcha(model: @user)