Version 0.10.107

+ view.qml:
  + if there is now active tariff during tariffs update, first one should be selected
  + updated components positioning and size
+ ticket.py:
  + updated explanation for enabled tariffs
  + Ticket.create should now bubble up False value of response argument and None, when
    there was an error during response parsing.
    Since DB.query returns False only when there was an error during network communication,
    its a safe way to differ between communication error and absence of a given Ticket
    in database.
+ tariff.py:
  + Implemented PrepaidTariff
  + Fixed bug for SubscriptionTariff.calc.
  + Implemented doctests for SubscriptionTariff and PrepaidTariff.
+ payments.py
  + Reader now differs between absence of a given ticket in database and communication
    error during network request.
+ card.py:
  + date formats moved to config.py
  + added support for PrepaidTariff in Card.pay.
  + card payment has been refactored to use unicode representation of
    tariff.calc result.