Use pre tags for view source to preserve newlines.

- Fixes #299

ui/src/components/comment-node.tsx

@@ -112,7 +112,7 @@ export class CommentNode extends Component<CommentNodeProps, CommentNodeState> {
           {this.state.showEdit && <CommentForm node={node} edit onReplyCancel={this.handleReplyCancel} disabled={this.props.locked} />}
           {!this.state.showEdit && !this.state.collapsed &&
             <div>
-              {this.state.viewSource ? <div>{this.commentUnlessRemoved}</div> : 
+              {this.state.viewSource ? <pre>{this.commentUnlessRemoved}</pre> : 
               <div className="md-div" dangerouslySetInnerHTML={mdToHtml(this.commentUnlessRemoved)} />
               }
               <ul class="list-inline mb-1 text-muted small font-weight-bold">

ui/src/components/post-listing.tsx

@@ -309,7 +309,7 @@ export class PostListing extends Component<PostListingProps, PostListingState> {
           }
             {this.props.showBody && post.body &&
               <>
-                {this.state.viewSource ? <div>{post.body}</div> : 
+                {this.state.viewSource ? <pre>{post.body}</pre> : 
                 <div className="md-div" dangerouslySetInnerHTML={mdToHtml(post.body)} />
                 }
               </>