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)