Layouts: add preset layouts and customized layout
Preset layouts: According the edit workflow we should have 6:
- "assembly - logging"
- "editing"
- "audio"
- "effects".
- "color correction"
- "graphics - title". Maybe we can make the title windows "docable" as well.
Add an indicator which layout is active. Maybe on the program "banner" 
User layouts: Possibility that the user can add new layouts and save changed layouts under a separate name:
- "new layout"
- "delete layout"
- "reset current layout"
- "import layout from projects" (default)
On the end we would have 6 given standard layouts and the user can change and add layouts as he likes.
see here: https://bugs.kde.org/show_bug.cgi?id=356493
Save layout in a specific file: $HOME/.config/kdenlive-layoutsrc (commit 39799e91)