Instantiate the layout manager with a test component in the visualise view

- In the rest of the MainVisualise take all the available space for Flexlayout and the layout manager.
- getInstance from the layout manager to be displayed in the main visualise
- by default have one test component opened
- when you drag, the test component should display the list of all the items that have been dragged inside
- style the flexlayout and the test component, the test component will be later the wrapper for the plot components.
- implement the + custom icon to open another test component