Due date setting context
A special context should be added to allow setting due date for an issue.
User: Set due date of #1076 to 21 October
Alos the context should support the following queries:
User: I must finish #1076 in 7 days
This way user won’t need to calculate the due date - Orangutan will do this for him/her (of course, Orangutan should count only work days by default).