refactor: sketches page

- Added new widget SketchTeaser
- Moved get_recent_sketches as static method in LMSSketch
- Added `models.py` to make it easy to import Course and Sketch class
- Updated the sketches template to use the SketchTeaser widget

community/public/css/style.css

@@ -291,4 +291,26 @@ nav.navbar {
 .message-section {
   margin-left: 5%;
   display: inline-block;
-}
+}
+
+.sketch-preview {
+  background: white;
+  border-radius: 10px;
+  border: 1px solid #ddd;
+  width: 220px;
+}
+
+.sketch-preview svg {
+  width: 200px;
+  height: 200px;
+}
+
+.sketch-image {
+  background: white;
+  padding: 10px;
+}
+
+.sketch-footer {
+  padding: 10px;
+  background: #eee;
+}