fix widget-import-warning test

wasn't updated with warning changes
Merge pull request #7211 from minrk/warning-test

fix widget-import-warning test
Add kernel resources directory to package_data
Remove outdated path from MANIFEST.in

package_data seems to be included in the sdist automatically, so no need
to specify schema files etc.
Merge pull request #7212 from takluyver/kernelspec-package-data

Add kernel resources (logos) to package_data