refactor styles and structure for wompum components; improve grid spacing and layout

static/js/wompum.js

@@ -137,7 +137,8 @@ class ArticleGrid extends WompumGrid {
             else if (column >= this.gridSize.columns - facilitatorColumns) section = 'facilitator';
             else section = 'subject';
             
-            cell.className = 'wompum-cell';
+            // Use BEM modifiers for sections
+            cell.className = `wompum-cell wompum-cell--${section}`;
             cell.setAttribute('data-cell-index', i);
             cell.setAttribute('data-section', section);
             cell.setAttribute('data-column', column);