Fixes from frontend/backend url separation (#1829)

* Fixes from frontend/backend url separation

This fixes the CORS and CSP headers.

Also, in thie commit, I removed the cors_supports_credentials config parameter,
which was recently introduced.
Instead, the logic determines the need to use CORS headers if the
web_page_url is set.

 #1778

server/cli/launch.py

@@ -296,7 +296,7 @@ class CliLaunchServer(Server):
             "application/octet-stream",
         ]
         Compress(app)
-        if app_config.server_config.app__cors_supports_credentials or app_config.server_config.app__debug:
+        if app_config.server_config.app__debug:
             CORS(app, supports_credentials=True)