Resolve "Implement basic functionality"

Closes #1 (closed) Closes #2 (closed) Closes #3 (closed) Closes #4 (closed) Closes #5 (closed) Closes #6 (closed)

src/Grid.vue

@@ -17,6 +17,7 @@
       :h="item.h"
     >
     </DragContainer>
+    <slot></slot>
   </div>
 </template>
 
@@ -56,7 +57,7 @@ export default {
           }
         }
       }
-      if (this.posValidation) return this.posValidation(x, y);
+      if (this.posValidation) return this.posValidation(x, y, key);
       return true;
     },
     handleDragOver(event) {