Partitioning

GephiLite can propose special features for partitioned networks (multipartite graph without the constraints of no inter-partite edges).
Partitioned only work on nodes. Partitions on edge are totally possible too. It does feel like a very advanced feature though which brings us a little bit beyond tthe "Lite" scope. But it will break coherence not to do it and it has a usage we keep it but we might hide edge partitioning a little bit more than node partitioning in the UI.

- [x] a UI block on top of appearance allows the user to activate the partitioning feature by selecting a partition data attribute to work on
- [x] A edge/node mode selector (to be defined later)

When a partitioning is active
- [ ] option to add labels to replace value by proper text to be used in captions including null/undefined values cases. (Note such a dictionary is editable also from appearance.caption module (see #5)
- [ ] if there is an active selection add a button to create a partition group for this group of node/edge. This button opens a modal which solves the what to do questions such as:
- [ ] if a partition is active: use the current partition or another one or a new one
- [ ] add a default value for others items not in the selection

- [ ] I can restrict a filter to a set of partitions (list of value in a field declared as a partition). In such a case the filter will apply only on the partition.s. The items (node/edges) not in the partitions are always kept.
- [ ] list the visual variables (size, color, labels) for edges by partition if active (see#19).
- [ ] partition label dictionaries

Start by reviewing the existing partitioning UI in Appearance and the related appearance.caption module referenced in issue #5. The issue lists several unfinished goals, including partition labels, selection-based partition groups, partition-restricted filters, and edge visual variables; done requires resolving their behavior and completing the corresponding UI.

Written by the indexing model from the issue text.