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

routers/repo/commit.go

@@ -245,6 +245,7 @@ func Diff(ctx *context.Context) {
 	}
 
 	ctx.Data["CommitID"] = commitID
+	ctx.Data["AfterCommitID"] = commitID
 	ctx.Data["Username"] = userName
 	ctx.Data["Reponame"] = repoName