Refactoring of gui and widget API for BEC CLI

Description

This MR refactoring reviewed and improved the CLI API for accessing BEC Widgets GUI instance. The refactoring also includes dock_areas and docks. This needs to be tested together with

Related Issues

closes #428

Type of Change

• dynamic namespace for dock_areas on gui.
• dynamic namespace for docks on gui.bec.
• dynamic namespace for widgets on gui.bec.my_dock_area.
• direct mapping of widget namespace on gui.bec.elements.
• renamed methods, cleaned up the namespace for GUI, DockAreas and Docks
• new method gui.connect_to_gui_server(gui_id:str) allows to connect to another GUIServer, and use the CLI to interact with it.
• There is also now a binding for all available widgets via gui.available_widgets.

Below is a snippet of the implementation

Potential side effects

All methods should be checked, I tried my best playing around.

Additional Comments

Definition of Done

• Add tests
• Clean up code
• Cherry pick **kwargs update for widgets.
• Documentation is up-to-date. (should we add the sketch to the docs, or rather not?)