Fix notebook URL opened in browser when redirect file not used

[randomir]

Fix #1325.

With notebook~=7.0 ServerApp is responsible for launching browser, not NotebookApp anymore. In notebook~=6.0, launch_browser will append notebook path for opening in browser even when use_redirect_file is set to false.

ServerApp used to do the same, last time in v1.3.0. The change in behavior/bug seems to be introduced in 1bbcbcb359, released as 1.4.0.

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[randomir]

If this PR is on the right track, I can try adding some tests. Lmk.

[blink1073]

Hi @randomir, this seems like a reasonable change to me. @afshin, since you made the original change, do you agree?

[Zsailer]

Hi @randomir, this seems like a reasonable change to me. @afshin, since you made the original change, do you agree?

This looks right to me. @randomir do you want to take a crack at writing a test? Otherwise, I can take this PR over to get it merged.

[randomir]

@Zsailer, thanks for taking a look. I can take a crack at writing a test, and then ping you when I think it's ready for review.

[Zsailer]

Great! thanks @randomir! Let me know if you need any help or have any questions around our unit tests.

[DanielGoldfarb]

From my perspective, it appears this is not limited to notebooks but to jupyterlab as well. It appears that the jupyter lab command does not see or respond to c.ServerApp.use_redirect_file=False by sending http://localhost:8889/?token=... to the browser (instead of sending file:///...)

With this PR, will jupyter lab now respect c.ServerApp.use_redirect_file=False?
If yes, when will this be merged?
If no, can you please clarify for me? Is there a different config to be able to get jupyter lab to not use a redirect file but rather send http://localhost:8889/?token=...?

Thank you.