Redesign the app's container in aiidalab home (aiidalab#985)

This PR uses new CSS classes introduced in aiidalab/aiidalab-home#190 to redesign the app's container in the home app.

start.py

@@ -2,21 +2,45 @@
 
 
 def get_start_widget(appbase, jupbase, notebase):  # noqa: ARG001
-    return ipw.HTML(
-        f"""
-        <table>
-        <tr>
-        <th style="text-align:center">Utils</th>
-        <tr>
-        <td valign="top"><ul>
-            <li><a href="{appbase}/job_list.ipynb" target="_blank">Job History</a></li>
-            <li><a href="{appbase}/plugin_list.ipynb" target="_blank">Plugins</a></li>
-        </ul></td>
-        </tr>
-        </table>
-    <div align="center">
-        <a href="{appbase}/qe.ipynb" target="_blank">
-            <img src="https://gitlab.com/QEF/q-e/raw/develop/logo.jpg" height="120px" width=243px">
-        </a>
-    </div>"""
-    )
+    return ipw.HTML(f"""
+        <div class="app-container">
+            <a href="https://www.quantum-espresso.org/" target="_blank">
+                <img
+                    src="https://gitlab.com/QEF/q-e/raw/develop/logo.jpg"
+                    height="180px"
+                    width=323px">
+            </a>
+            <div class="features">
+                <a
+                    class="feature"
+                    href="{appbase}/qe.ipynb"
+                    target="_blank">
+                    <img
+                        class="feature-logo"
+                        src="{appbase}/miscellaneous/logos/workbench.png"
+                        alt="New calculation" />
+                    <div class="feature-label">New calculation</div>
+                </a>
+                <a
+                    class="feature"
+                    href="{appbase}/job_list.ipynb"
+                    target="_blank">
+                    <img
+                        class="feature-logo"
+                        src="{appbase}/miscellaneous/logos/history.png"
+                        alt="Calculation history" />
+                    <div class="feature-label">Calculation History</div>
+                </a>
+                <a
+                    class="feature"
+                    href="{appbase}/plugin_list.ipynb"
+                    target="_blank">
+                    <img
+                        class="feature-logo"
+                        src="{appbase}/miscellaneous/logos/plugins.png"
+                        alt="Plugin store" />
+                    <div class="feature-label">Plugin store</div>
+                </a>
+            </div>
+        </div>
+    """)