Add database import in progress message

data/interfaces/default/history.html

@@ -8,6 +8,13 @@
 
 <%def name="body()">
 <div class='container-fluid'>
+    % if config['database_is_importing']:
+    <div style="text-align: center; margin-top: 20px;">
+        <i class="fa fa-refresh fa-spin"></i>&nbsp; Tautulli is importing history from another database. This could take a few minutes depending on the size of your database.
+        <br />
+        You may leave this page and check back later.
+    </div>
+    % endif
     <div class='table-card-header'>
         <div class="header-bar">
             <span><i class="fa fa-history"></i> History</span>