Implements request #14320 The rendering of CSV files does match the diff style.
* Moved CSV logic into base package.
* Added method to create a tabular diff.
* Added CSV compare context.
* Added CSV diff template.
* Use new table style in CSV markup.
* Added file size limit for CSV rendering.
* Display CSV parser errors in diff.
* Lazy read single file.
* Lazy read rows for full diff.
* Added unit tests for various CSV changes.
* Implemented "Reference in new issue"
* Fixed menu style on "pulls/x/files" because "button" has a style.
* Added context menu for PR file comments.
* Use only a single modal for every comment.
* Use current repository as default. Added search filter.
* Added suggested changes.
* Fixed assignment.
Co-authored-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: 6543 <6543@obermui.de>
