[Feature]: Add "Elements" tab and allow grouping

### Feature Request

I think it would be seriously helpful if "Graphs", "Graph Info", "Project" would be extended by an "Elements" or "Nodes" tab

Use-cases which come spontaenously to my mind:
- Easier selection of elements
- Allows grouping/ungrouping of elements to move them around hazzle free
- Element inspection to see additional information (id, type etc.). You can currently only seeing that by inspecting elements in dev-tools or opening the file
- If this would show all graphs and their elements (not just the current graph ones), you could easier move elements or groups of elements from graph A to graph B (just drag & drop). And you would also not have an issue if they overlap other elements after insertion, as you can just select the group in elements and move them.

Just some rough ideas. I really think "grouping" would be very helpful. But I am not sure it is a good idea without the option to be able to see the groups somewhere.

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct

Start by reviewing the existing “Graphs”, “Graph Info”, and “Project” tabs and how elements are selected. Clarify whether the first milestone is an Elements/Nodes view, grouping and ungrouping, inspection, cross-graph movement, or some combination. Done should include an agreed scope and a way to view and manipulate the relevant elements.

Written by the indexing model from the issue text.