Admin can add a link to a page where someone sells this series

[php-coder]

When admin opens page with series info, he should see the form with the header "Add info about selling" and the following fields/labels:

• Date: optional text field, accept value in format 12.10.2012, date must be in past
• Seller: required <select> field, the values are populated from the transaction_participants table
• Url: optional text field. We can try to use <input type="url">. Let's try to use special validation annotation from the hibernate-validator
• Price: price and currency: required fields.
• Alternative price/currency: optional fields.
• Buyer: optional <select> field.

Additional validation:

• buyer and seller should be different
• price and alternative price should be different

Things to not forget:

• Protect by togglz and spring security
• Protect URL for form submission by Spring Security