Ability to filter/ignore diff lines using regexp

Description

Often, a large MR will contain changes that are boilerplate of comparatively little interest. It would be nice to have a way to ignore them, so as to concentrate on the business logic.

Example: Java needs import lines and modern IDEs mostly take care of them. But changes in those lines are hardly ever relevant for code review. It would be great if one could ignore changes in lines matching ^(import|package). If a file had only that kind of change, it might be even omitted from the list.

Proposal

• Have a 'Show only lines matching _______ [ OK ]' at the top of the diff pane
• Have a 'Don't show lines matching _______ [ OK ]' at the top of the diff pane
• The diff should only show the lines that pass both filters
• The filters should be regexp based
• If a file doesn't have any lines passing the filters, remove it from the list