Added trytond-gift-card as a dependency #6000


![gc_1](https://cloud.githubusercontent.com/assets/3972835/5000078/2b51cad2-6a0e-11e4-9401-2f9bea201816.png)

![gc_2](https://cloud.githubusercontent.com/assets/3972835/4999261/ca42c25c-6a06-11e4-98de-6f19560178a9.png)

also check if open amount is allowed, if not the amount should be in one of the allowed denominations