Base time remaining on end date of active sprint

[fniessink]

Is your feature request related to a problem? Please describe.
Some metrics need to be fixed before the end of the sprint. But Quality-time has no awareness of the end (and start) of sprints.

Describe the solution you'd like
Allow for specifying per metric that the time remaining should be based on the end of the active sprint. The user can indicate this when accepting technical debt and setting the technical debt end date: instead of selecting a date from the calendar Quality-time offers an option to use the end date of the active sprint.

Describe alternatives you've considered
Manually setting the time remaining.