Add model previews on upload (#27)

Closes #22

This modifies the upload form to allow for a preview of models.

Reviewed-on: #27

extension.json

@@ -14,6 +14,7 @@
 	    "model/gltf-binary": "MediaWiki\\Extension\\GlModelViewer\\GlModelHandler"
     },
     "Hooks": {
+        "UploadFormInitDescriptor": "MediaWiki\\Extension\\GlModelViewer\\GlModelHooks::onUploadFormInitDescriptor",
         "MimeMagicInit": "MediaWiki\\Extension\\GlModelViewer\\GlModelHooks::onMimeMagicInit",
         "MimeMagicImproveFromExtension": "MediaWiki\\Extension\\GlModelViewer\\GlModelHooks::onMimeMagicImproveFromExtension",
         "BeforePageDisplay": "MediaWiki\\Extension\\GlModelViewer\\GlModelHooks::onBeforePageDisplay",
@@ -38,6 +39,14 @@
 				"mediawiki.util",
 				"mediawiki.api"
 			]
+        },
+        "ext.glmv.upl": {
+            "styles": [
+                "glmv-upl.css"
+            ],
+            "packageFiles": [
+                "glmv-upl.js"
+            ]
         }
     }
 }