Debuggable interface

[jtpio]

The notebook and console handlers share similar code when it comes to handling cells and editors:

debugger/src/handlers/notebook.ts

Lines 69 to 84 in d3f43e5

	private _addEditorHandler(cell: Cell) {
	const modelId = cell.model.id;
	if (cell.model.type !== 'code' || this._cellMap.has(modelId)) {
	return;
	}
	const codeCell = cell as CodeCell;
	const editorHandler = new EditorHandler({
	debuggerService: this._debuggerService,
	editor: codeCell.editor
	});
	codeCell.disposed.connect(() => {
	this._cellMap.delete(modelId);
	editorHandler.dispose();
	});
	this._cellMap.set(cell.model.id, editorHandler);
	}

We could investigate how to make them more generic, for example by implementing a common interface.