Added post roll to timelapse

You can now define an amount of seconds that should be added to the rendered timelapse (so, since the current fps setting is 25 frames per seconds, 25 * the configured amount of post roll seconds images will need to be captured).

Timed timelapses add this to the actual run time of the timelapse capturing process (so if you configure 1s post roll, a timed timelapse will run 25s longer than the print)

Z-triggered timelapses just create one last capture from the webcam and use this image again and again (so 25 times for a post roll of 1s).

Implements #384