Merge pull request
#1621 from ivanov/clear-input-prompt-on-clear-all-output...
Merge pull request
#1621 from ivanov/clear-input-prompt-on-clear-all-output
clear In[] prompt numbers on "Clear All Output"
For more version-control-friendly `.ipynb` files, this strips the `In[]` prompt numbers when doing a "Clear all output". This reduces the amount of noise in commit-to-commit diffs that would otherwise show the (highly variable) prompt number changes.
