Version 0.10.92

+ payments module refactored to support new payable concept:
  + payable concept contract consists of a single method:
    @pyqtSlot(QObject, result=QObject)
    def pay(self, tariff):
     'returns QObject that must conform to Payment concept'
     ...
    Obviously, class that implements payable concept must inherit QObject.
    This change has been inspired by adding support for contactless cards,
    to make tickets an contactless cards behave in a same way from the Payments
    point of view.
+ all payments should now conform to new concept requirements:
  + Added vfcd_explanation method to payment contract.
    This method should return a list of two unicode strings
    that will subsequently be displayed on Vacuum Fluorescent
    Customer Display when its payment is being viewed.
+ tariff module update:
  + implemented SubscriptionTariff.
+ card module refactored out of db  module.
  + Card class adapted to its new payable role.
  + implemented payment facilities for Card class (subcription tariffs only).
+ ticket module update:
  + Added tariff detection to Ticket.pay + new payment type for this case.
  + Non-stub ticket payments now conform to new payment contract requirements.
+ db.DB module got generate_payment method, that adds record to Payment table in
  remote database for every currently present payment type.
+ view.qml has been adapted to payable concept
  + now displaying Tariff.maxPerDay.