Investigate purpose of total_balance hidden field in group orders and try to remove it

[lentschi]

See

foodsoft_hackathon/app/views/group_orders/_form.html.haml

Line 200 in bb044e6

%input#total_balance{name: "total_balance", type: "hidden", value: @ordergroup.account_balance - @group_order.price}/

and

foodsoft_hackathon/app/assets/javascripts/group-order-form.js

Line 57 in bb044e6

this.totalBalance$.val(I18n.l('currency', balance));

Shouldn't this be calculated in the backend?