Display assignments

[lpatiny]

Assignments can be done at the level of a range or at the level of the signal.

Currently only the one at the level of the range can be displayed.

We would also need to display and edit the one at the level of the signal.

1. Rename the current label to 'Range assignment'

2. Add a new option for 'Signal assignment'

3. Display the signal assignment at the level of the multiplicity label (the little tree) and give the possibility to edit it.