Invoice enter modal now saves invoices.

client/src/graphql/invoices.queries.js

@@ -0,0 +1,11 @@
+import { gql } from "apollo-boost";
+
+export const INSERT_NEW_INVOICE = gql`
+  mutation INSERT_NEW_INVOICE($invoice: [invoices_insert_input!]!) {
+    insert_invoices(objects: $invoice) {
+      returning {
+        id
+      }
+    }
+  }
+`;