Adds framework for "server health" display

- Adds global context object "system_healthy" (boolean)
- Framework for running system health checks
- Updated system info forms
- Displays warning next to user menu if system health errors exist

(cherry picked from commit ce6d626ab39147fc389de90815ca8baae2385d82)

InvenTree/templates/about.html

@@ -16,11 +16,6 @@
                 <div>
                     <table class='table table-striped table-condensed'>
                         <col width='25'>
-                        <tr>
-                            <td></td>
-                            <td>{% trans "Instance Name" %}</td>
-                            <td>{% inventree_instance_name %}</td>
-                        </tr>
                         <tr>
                             <td><span class='fas fa-hashtag'></span></td>
                             <td>{% trans "InvenTree Version" %}</td><td><a href="https://github.com/inventree/InvenTree/releases">{% inventree_version %}</a></td>

InvenTree/templates/navbar.html

@@ -52,7 +52,11 @@
             </button>
           </li>
           <li class='dropdown'>
-            <a class='dropdown-toggle' data-toggle='dropdown' href="#"><span class="fas fa-user"></span> <b>{{ user.get_username }}</b></a>
+            <a class='dropdown-toggle' data-toggle='dropdown' href="#">
+              {% if not system_healthy %}
+              <span title='{% trans "InvenTree server issues detected" %}' class='fas fa-exclamation-triangle icon-red'></span>
+              {% endif %}
+              <span class="fas fa-user"></span> <b>{{ user.get_username }}</b></a>
             <ul class='dropdown-menu'>
                 {% if user.is_authenticated %}
                 {% if user.is_staff %}
@@ -65,8 +69,15 @@
                 <li><a href="{% url 'login' %}"><span class="fas fa-sign-in-alt"></span> {% trans "Login" %}</a></li>
                 {% endif %}
                 <hr>  
+                <li id='launch-stats'><a href='#'>
+                  {% if system_healthy %}
+                  <span class='fas fa-server'>
+                  {% else %}
+                  <span class='fas fa-exclamation-triangle icon-red'>
+                  {% endif %}
+                  </span> {% trans "System Information" %}
+                </a></li>
                 <li id='launch-about'><a href='#'><span class="fas fa-info-circle"></span> {% trans "About InvenTree" %}</a></li>
-                <li id='launch-stats'><a href='#'><span class='fas fa-chart-pie'></span> {% trans "Statistics" %}</a></li>
               </ul>
             </li> 
       </ul>

InvenTree/templates/stats.html

@@ -4,6 +4,33 @@
 
 <table class='table table-striped table-condensed'>
     <col width='25'>
+
+    <tr>
+        <td colspan="3"><b>{% trans "Server" %}</b></td>
+    </tr>
+    <tr>
+        <td><span class='fas fa-server'></span></td>
+        <td>{% trans "Instance Name" %}</td>
+        <td>{% inventree_instance_name %}</td>
+    </tr>
+    <tr>
+        <td><span class='fas fa-exclamation-triangle'></span></td>
+        <td>{% trans "Server status" %}</td>
+        <td>
+            {% if system_healthy %}
+            <span class='label label-green'>{% trans "Healthy" %}</span>
+            {% else %}
+            <span class='label label-red'>{% trans "Issues detected" %}</span>
+            {% endif %}
+        </td>
+    </tr>
+
+    {% if not system_healthy %}
+    {% for issue in system_issues %}
+    <!-- TODO - Enumerate system issues here! -->
+    {% endfor %}
+    {% endif %}
+
     <tr>
         <td colspan='3'><b>{% trans "Parts" %}</b></td>
     </tr>