Remember last-visited Attract project in session

This allows us to keep rendering the "Shots" and "Assets" links in the
sidebar, even when someone navigates away from the project scope.

attract/routes.py

@@ -1,7 +1,7 @@
 import functools
 import logging
 
-from flask import Blueprint, render_template, redirect, url_for, request, jsonify
+from flask import Blueprint, render_template, redirect, url_for, request, jsonify, session
 import flask_login
 import werkzeug.exceptions as wz_exceptions
 
@@ -131,6 +131,8 @@ def attract_project_view(extra_project_projections: dict=None, extension_props=F
             if not is_attract:
                 return error_project_not_setup_for_attract()
 
+            session['attract_last_project'] = project.to_dict()
+
             # Check user access.
             auth = current_attract.auth
             auth.determine_user_rights(str2id(project['_id']))