Stores inputs in memory instead of in textareas.

Allow selecting multiple files.
Allow drag and dropping multiple files.
Clear all IO button will close all tabs.
Will now spawn multiple loaderworkers simultaneously.
Improve tab logic to break less and work in Firefox.

src/web/stylesheets/layout/_io.css

@@ -6,7 +6,7 @@
  * @license Apache-2.0
  */
 
-.input-text,
+#input-text,
 #output-text,
 #output-html {
     position: relative;
@@ -30,12 +30,6 @@
     -moz-padding-start: 1px; /* Fixes bug in Firefox */
 }
 
-#multi-input-wrapper {
-    display: flex;
-    flex-direction: column;
-    height: calc(100% - var(--title-height));
-}
-
 #input-tabs ul {
     list-style: none;
     background-color: var(--title-background-colour);
@@ -69,16 +63,21 @@
 
 .active-input-tab {
     font-weight: bold;
+    background-color: var(--primary-background-colour);
 }
 
 .input-tab-content {
     width: 100%;
+    max-width: 100%;
     padding-left: 5px;
     padding-right: 5px;
     padding-top: 10px;
     padding-bottom: 10px;
     height: var(--tab-height);
     vertical-align: middle;
+    overflow: hidden;
+    white-space: nowrap;
+    text-overflow: ellipsis;
 }
 
 .btn-close-tab {
@@ -89,7 +88,7 @@
 
 .textarea-wrapper {
     width: 100%;
-    height: 100%;
+    height: calc(100% - var(--title-height));
     box-sizing: border-box;
     overflow: hidden;
     pointer-events: auto;
@@ -102,21 +101,13 @@
     color: var(--fixed-width-font-colour);
 }
 
-.input-wrapper {
-    display: none;
-}
-
-.active-input-area {
-    display: inline-block;
-}
-
 #input-highlighter,
 #output-highlighter {
     position: absolute;
     left: 0;
-    bottom: 0;
+    top: 0;
     width: 100%;
-    height: calc(100% - var(--title-height));
+    height: 100%;
     padding: 3px;
     margin: 0;
     overflow: hidden;
@@ -167,13 +158,13 @@
     transition: all 0.5s ease;
 }
 
-.input-file,
+#input-file,
 #output-file {
     position: absolute;
     left: 0;
     bottom: 0;
     width: 100%;
-    height: calc(100% - var(--tab-height) - var(--title-height));
+    height: calc(100% - var(--title-height));
     display: none;
 }
 
@@ -213,7 +204,6 @@
 
 .dropping-file {
     border: 5px dashed var(--drop-file-border-colour) !important;
-    margin: -5px;
 }
 
 #stale-indicator {