Added status message mechanism for the Worker to report to the app

src/web/stylesheets/layout/_io.css

@@ -110,3 +110,11 @@
     font-weight: normal;
     cursor: help;
 }
+
+#output-loader .loading-msg {
+    opacity: 1;
+    font-family: var(--primary-font-family);
+    line-height: var(--primary-line-height);
+    color: var(--primary-font-colour);
+    top: 50%;
+}

src/web/stylesheets/preloader.css

@@ -58,7 +58,7 @@
     animation: spin 1.5s linear infinite;
 }
 
-#preloader-msg {
+.loading-msg {
     display: block;
     position: relative;
     width: 300px;
@@ -69,14 +69,14 @@
     opacity: 0;
 }
 
-#preloader-msg.loading {
+.loading-msg.loading {
     opacity: 1;
     transition: all 0.1s ease-in;
 }
 
 
 /* Loaded */
-.loaded #preloader-msg {
+.loaded .loading-msg {
     opacity: 0;
     transition: all 0.3s ease-out;
 }