Added the ability to manually add or remove money from piggy banks (issue #6) [skip ci]

app/models/Account.php

@@ -92,6 +92,14 @@ class Account extends Ardent
         return $this->hasMany('Transaction');
     }
 
+    /**
+     * @return \Illuminate\Database\Eloquent\Relations\HasMany
+     */
+    public function piggybanks()
+    {
+        return $this->hasMany('Piggybank');
+    }
+
     /**
      * @param \Carbon\Carbon $date
      *