Ignore some traits in shim layer

[afshin]

Adds a list of traits that should be ignored by nbclassic's shim layer.

• open_browser is now a trait of jupyter_server's ServerApp and ExtensionApp. These traits must have the same name for backward-compatibility.
• log_level and log_format exist in ServerApp, ExtensionApp, and NotebookApp, and users need to be able to configure each one separately.

This PR also changes the name trait of nbclassic's NotebookApp to "notebook". This enables nbclassic to find the jupyter_notebook_config.py