Make DragDrop entirely clickable (#1633)

* /examples/dev - added drag-drop plugin dev environment

* @uppy/drag-drop - moved isDragDropSupported() to @uppy/utils

* @uppy/drag-drop - got rid of drag-drop npm library

* examples/dev - made compiled files placed in /output instead of /lib

* ~/examples/dev - made watchify only watch files once

* @uppy/drag-drop - add onPaste

* /examples/dev - readded html css override-attempts

* @uppy/drag-drop - made whole area clickable, and made it accessible

* @uppy/drag-drop - removed excessive outline in firefox

* change dragText classname to browse, minor spacing and order changes

examples/dev/DragDrop.html

@@ -10,13 +10,16 @@
       main {
         text-align: center;
         margin: 20px auto;
-        width: 400px;
+        max-width: 400px;
       }
     </style>
     <main class="foo">
       <h1>Drag-drop is here</h1>
+
+      <input type="text"/>
       <div id="uppyDragDrop"></div>
       <div id="uppyDragDrop-progress"></div>
+      <input type="text"/>
     </main>
 
     <link href="uppy.min.css" rel="stylesheet">