Expand/Collapse Files and Blob Excerpt while Reviewing/Comparing code (#8924)
* update #8659 fold/unfold code diffs
* add fold button style
* update #8659 implement expand up/down codes (blob excerpt)
* fix golint errors
* fix expand direction
* remove debug message
* update css style for blob exceprt
* fix typo in comment
* update style sheet with less
* update expect diff (add SectionInfo)
* update #8942 accept suggested change (fix typo)
* close reader and check file type before get tail section
* adjust button position and check file type before insert fold button
* move index js to web_src
* merge index.js with master
* generate index.js
* update js coding style
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