First attempt at account specific bill report.

app/Repositories/Bill/BillRepositoryInterface.php

@@ -77,6 +77,15 @@ interface BillRepositoryInterface
      */
     public function getBills();
 
+    /**
+     * Gets the bills which have some kind of relevance to the accounts mentioned.
+     *
+     * @param Collection $accounts
+     *
+     * @return Collection
+     */
+    public function getBillsForAccounts(Collection $accounts);
+
     /**
      * @param Bill $bill
      *