[#62691508] prevent option_line with quantity zero

Squashed commit of the following:

commit e5911d848e465b4413f4a244b57d057dd00cbc51
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Tue May 27 12:51:31 2014 +0200

    accepting only integers greater than zero as option_line quantity in hand_over

commit 62c68f9e62a1aee538aea0dd45830010beca7385
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Mon May 26 17:32:22 2014 +0200

    testing with contract_line quantity validation greater than zero