Fix odd looking uploaded main images (#612)

* fix thumbnail image height instead of width

* center uploaded main images

Co-authored-by: Jeffrey Warren <jeff@unterbahn.com>

Author: daemon1024

dist/PublicLab.Editor.css

@@ -181,6 +181,8 @@
   height: 180px;
   width: 720px;
   margin-bottom: 10px;
+  display: flex;
+  justify-content: center;
 }
 
 .mainImageBox.dragDrop {

src/modules/PublicLab.MainImageModule.js

@@ -25,10 +25,10 @@ module.exports = PublicLab.MainImageModule = PublicLab.Module.extend({
         _module.image.onload = function() {
           var heightDropdown = this.height;
           var widthDropdown = this.width;
-          if (this.width > 340) {
-            var aspectRatio = this.width / 340;
-            widthDropdown = 340;
-            heightDropdown = this.height / aspectRatio;
+          if (this.height > 180) {
+            var aspectRatio = this.height / 180;
+            widthDropdown = this.width / aspectRatio; ;
+            heightDropdown = 180;
           }
           _module.dropEl.css('height', heightDropdown);
           _module.dropEl.css('width', widthDropdown);