ramiz hajj

(4a -> 4) Add menu to assign an `Instance` to an `InstanceGroup`

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# Add menu to assign an `Instance` to an `InstanceGroup` - [x] Create a `sessionsMenu` named "Sessions" (similar to the [`tracksMenu`](https://github.com/talmolab/sleap/blob/936663efea79b0de8dfd4695619ad8e3298e55d0/sleap/gui/app.py#L815)) - [x] Add a `self.inst_groups_menu` attribute to the `MainWindow`...

### Description [Bug fix in docks.py and cameras.py] ### Types of changes - [ ] Bugfix - [ ] New feature - [ ] Refactor / Code style update (no...

Create and assign instance group with Shift + `num` in (`n_instance_groups`, `9`]

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### Description When the user clicks Shift + 0 keyboard shortcut, it should both create a new instance group and assign the selected instance if any. ### Types of changes...