If a track is missing by insert a clip we should create the missing track

STEPS TO REPRODUCE

1. Add a clip to the timeline where you haven’t enough audio or video tracks
2. On the bottom left a warning pop up:
3. User has to create the missing track first

OBSERVED RESULT
User are confused why he cannot add the clip

EXPECTED RESULT
Kdenlive should create the missing track automatically (specially the audio track).
Or ask the user if he would like to add the missing video/or/audio track as well.

See here: https://www.youtube.com/watch?v=GuM72yJPtnE&t=2m14s