In diff viewer, add option to ignore empty lines

Currently, diff viewer already allows to ignore whitespace changes and case changes.

I suggest to add another option to ignore empty line changes.

Changing empty lines is very common refactoring that is hard to do wrong, therefore I'd like to not see these while reviewing changes, so I can pay more attention to what's important.

It would be OK if you simply don't color these lines without changing the actual comparison algorithm, ie it would be enough for me to "don't show" vs "ignore"