give hint on where to find custom.js
fallback on copy, copyfile if copy2 fails

in notebook manager
do not install less sources

only their css build results are used after install
only catch errors in copystat
Merge pull request #5357 from minrk/smb-fails

catch exception in copystat
fix docs, closes #5345
Merge pull request #5346 from hmeine/custom_js_docs

give hint on where to find custom.js
Merge pull request #5359 from minrk/no-install-less

do not install less sources
Suppress output even when a comment follows ;. Fixes #4525.
Merge pull request #5394 from ivanov/backtick-docs

nbconvert doc update
Merge pull request #5388 from shashi/semicolon-fix

Suppress output even when a comment follows ;. Fixes #4525.