REST API: Added file download URL to listing of attachments of a board.

Thanks to xet7 !

Related #1482

models/boards.js

@@ -1779,6 +1779,8 @@ if (Meteor.isServer) {
             attachmentId: doc._id,
             attachmentName: doc.original.name,
             attachmentType: doc.original.type,
+            url: FlowRouter.url(doc.url()),
+            urlDownload: `${FlowRouter.url(doc.url())}?&download=true&token=`,
             cardId: doc.cardId,
             listId: doc.listId,
             swimlaneId: doc.swimlaneId,