IT2 properties for Userstory

New Methods:
getIsExecutable() directly on Userstory (removed from
UserstorySessionFacade)
int getExpectedEffort()
int getRemainingEffort()
int getRemainingEffortPercent() (0-100)
void setPostponingReason()
String getPostponingReason

Removed Methods:
void setResponsible()
void setDue()
void getDue()