Complete move to PlotGrid #541

We want to remove the old plotting widget and fully move to a plot-grid based architecture. There are a number of outstanding tasks:

• Add small widget to add new plot-grids (a new tab). This needs to allow configuring the tab title as well as the grid size (2x2, 3x2, 3x3, ...). We probably need to generate a unique ID in addition to the display title.
• Add mechanism to persist plot grids configs. This will work hand-in-hand with the new JobOrchestrator (Job orchestrator #540), which will move the UI towards a workflow-based approach.
• Add mechanism to replace plots in the grids via the controller, e.g., if a job-transition for a workflow happens via the JobOrchestrator.

The backbone to this would probably be a PlotOrchestrator (working title, time will tell if it should remain independent of PlottingController, but during the refactor we want the old mechanism to remain functional so adding a fresh class seems benefitial). Conceptually it would be something like:

@dataclass
class PlotTab:
    name: UUID
    title: str
    plots: tuple[corner1, corner2, WorkflowId, OutputName, PlotterConfig]  # better: dataclass(es)

class PlotOrchestrator:
    _plots: list[PlotTab]

Just like JobOrchestrator stores WorkflowConfig, PlotOrchestrator would store plotter configs and plots tabs.