Refactor login_required and add auth blueprint

Moved the login_required logic to a new utils.py for reuse. Added a new auth blueprint and registered it in app.py. Updated user blueprint to use the shared login_required function.

application/utils.py

@@ -0,0 +1,11 @@
+from flask_login import current_user
+from flask import redirect, url_for, flash
+
+
+def login_required():
+    if not current_user.is_authenticated:
+        return redirect(url_for("auth.login"))
+    if current_user.must_change_password:
+        flash("You have to change your password")
+        return redirect(url_for("auth.change_password"))
+    return