gh-7044: set TMPDIR to workingdir in tests
Change exception message
remove some custom css

mainly in navbars, where we were doing custom
things that bootstrap already did with classes.

This did require the removal of multiple class LESS inheritance for
navbar buttons, because it doesn't work properly. Seems like a LESS bug, but I'm not sure.
Fixes for _display_banner when creating new qtconsole tabs

* make sure _display_banner is set in FrontendWidget
* make sure _display_banner flag is passed in from console app
Merge pull request #7131 from helenst/qtconsole-fix-new-tab

Fixes for _display_banner when creating new qtconsole tabs
Merge pull request #7109 from minrk/navbar-css

remove some custom css
Merge pull request #7113 from jdemeyer/test_tmpdir

gh-7044: set TMPDIR to workingdir in tests
remove client side manager, will be shipped with jupyterdrive
Merge pull request #7133 from Carreau/remove-client-side-manager

remove client side manager, will be shipped with jupyterdrive
[pr6953-docs] update docstrings/whatsnew/shell.rst for env/set_env magic
[pr6953-docs] move change env_magic.md to .rst