Retiring of IsPrivate field for Impediments in Targetprocess 3.11.3

We have recently made a decision to deprecate private impediment and have all the impediment in the system public. Mode details and reasons behind this decision is available in our blog: https://www.targetprocess.com/blog/2017/03/deprecating-private-impediments/

IsPublic field is still a part of Imepdiment's model for backward compatibility reasons, but this field is not connected with any logic starting with the version 3.11.3.