The color-bar, color-picker (#492), timeline, tabs (#118), minieditor (#404), and tool-bar should be dockable windows that can be moved to any other position on the screen.

Review #250, t/933, t/1065, /5472

Tasks:

• Multiple native windows are required to drag-and-drop widgets to separated windows (Complete back-end integration with OS #139)
• Initial Dock widget to put widgets on each side, center, create subdocks (preview)
• Restore old layout configuration (color bar split pos, timeline pos, etc.) and migrate to new Dock layout
• Load/saving Dock layout
• Create & customize current layoout (drag-and-drop widgets, etc.)

Following work will be done in #5327