Clean up handling of config

[blink1073]

Companion to jupyterlab/jupyterlab#8950.

Moves handling of page_config here completely so it is dynamic.

[codecov-commenter]

Codecov Report

Merging #123 into master will decrease coverage by 1.21%.
The diff coverage is 25.73%.

@@            Coverage Diff             @@
##           master     #123      +/-   ##
==========================================
- Coverage   60.50%   59.28%   -1.22%     
==========================================
  Files          19       20       +1     
  Lines        1504     1572      +68     
==========================================
+ Hits          910      932      +22     
- Misses        594      640      +46     

Impacted Files	Coverage Δ
jupyterlab_server/config.py	24.61% <24.61%> (ø)
jupyterlab_server/handlers.py	69.38% <50.00%> (+15.79%)	⬆️

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[bollwyvl]

Awesome stuff here! By dynamic, does this mean config set after starting the server would update the defaults (with a page reload, presumably)? I'd really love a way for nbgitpuller to work with this in binder...

[blink1073]

By dynamic, does this mean config set after starting the server would
update the defaults (with a page reload, presumably)?

Yup!

[bollwyvl]

Awesome. Will have to think how this could be made to work the nbgitpuller...

[blink1073]

Released as jupyterlab_server-2.0.0b7