Configure default duration for newly created transitions

Review Request #128783 - Created Aug. 27, 2016 and submitted

The DiveO

This patch adds the ability to configure the default transition length for newly created transitions.
- new Kdenlive configure dialog element for configuring the transition default duration.
- correctly using the new configuration transition_duration instead of the old hard-coded 65 frames value.
- correctly handling cases where the start point of the transition would be less than the timeline beginning of 00:00:00:00; the transition then is set to start at 00:00:00:00.

Tested on Kubuntu 16.04LTS with latest backports updates installed for KF5 and Qt.

The DiveO
Review request changed

Status: Closed (submitted)

Change Summary:

Submitted with commit e1657298e7ec6dae4f864eae6cd6b0c15ace01ff by Jean-Baptiste Mardelle to branch Applications/16.08.