Render commit msg as header + verbatim description

Most commit in Git are expected to follow standard of single header line,
followed by description paragraphs, separated by empty line from previous block.

Previously Gogs were treating everything as single header. Now we are trying to
render only first line as header, but following lines (description chunks) as a
verbatim.

templates/repo/diff.tmpl

@@ -5,14 +5,12 @@
     {{if .IsDiffCompare }}
     {{template "repo/commits_table" .}}
     {{else}}
-    <h4 class="ui top attached info header">
-      <div class="ui right">
-        <a class="ui blue tiny button" href="{{EscapePound .SourcePath}}">
-          {{.i18n.Tr "repo.diff.browse_source"}}
-        </a>
-      </div>
-      {{RenderCommitMessage .Commit.Message $.RepoLink $.Repository.ComposeMetas}}
-    </h4>
+    <div class="ui top attached info clearing segment">
+      <a class="ui floated right blue tiny button" href="{{EscapePound .SourcePath}}">
+        {{.i18n.Tr "repo.diff.browse_source"}}
+      </a>
+      {{RenderCommitMessage true .Commit.Message $.RepoLink $.Repository.ComposeMetas}}
+    </div>
     <div class="ui attached info segment">
       {{if .Author}}
       <img class="ui avatar image" src="{{.Author.AvatarLink}}" />