Simplify the new template rendering

- No extra template code is required for any new page
- All loaded in base.html or page_base.html
- Oh, so clean!

InvenTree/templates/plugin/panel_content.html

@@ -0,0 +1,19 @@
+{% if plugin_panels %}
+<!-- Custom panel items, loaded via plugins -->
+{% for panel in plugin_panels %}
+<div class='panel panel-hidden' id='panel-{{ panel.key }}'>
+    <div class='panel-heading'>
+        <div class='d-flex flex-wrap'>
+            <h4>{{ panel.title }}</h4>
+            {% include "spacer.html" %}
+            <div class='btn-group' role='group'>
+                <!-- TODO: Implement custom action buttons for plugin panels -->
+            </div>
+        </div>
+    </div>
+    <div class='panel-content'>
+        {{ panel.content | safe }}
+    </div>
+</div>
+{% endfor %}
+{% endif %}

InvenTree/templates/plugin/panel_js.html

@@ -0,0 +1,10 @@
+{% if plugin_panels %}
+// Run custom javascript when plugin panels are loaded
+{% for panel in plugin_panels %}
+{% if panel.javascript %}
+onPanelLoad('{{ panel.key }}', function() {
+{{ panel.javascript | safe }}
+});
+{% endif %}
+{% endfor %}
+{% endif %}

InvenTree/templates/plugin/panel_menu.html

@@ -0,0 +1,6 @@
+{% if plugin_panels %}
+<!-- Custom sidebar menu items, loaded via plugins -->
+{% for panel in plugin_panels %}
+{% include "sidebar_item.html" with label=panel.key text=panel.title icon=panel.icon %}
+{% endfor %}
+{% endif %}