Auto-resize editor on input, so it doesn't scroll in its own window

Author: pabzm

plugins/markmirror/skins/elastic/styles/markmirror.less

@@ -28,7 +28,9 @@
 
 #markmirror-container {
     .cm-editor {
-        height: 45vh;
+        min-height: 45vh;
+        height: auto;
+        resize: vertical;
         border: solid thin @color-input-border;
         border-radius: .25rem;
     }