GUI: Viewparts of shared elements

As a user I would like to be able to restore the GUI to the default layout. Currently, viewparts containing a shared element exhibits some odd behaviour:
- if the shared element gets moved away (not just resized) from its original position in the application model (e.g. to a different part sash container), the space becomes blank and unusable. The shared element (or indeed any other viewpart) cannot be moved back into this space.
- Hitting the reset layout button does not reset PartStacks containing shared elements. Instead they keep whatever elements were in them at the time.
Once a shared element has been moved, it can't be restored to its original layout without restarting the GUI. This currently affects the scripting console (plus the matplotlib plot window after https://github.com/ISISComputingGroup/ibex_gui/pull/1053).

#### Steps to Recreate
1.Open the Scripting perspective
1. Move The Dashboard view into the Partstack that has "Console" in it (same tabbed container)
1. Click "Reset Layout"
1. You now have 2 dashboard containers. Reset layout will make the dashboard display in the usual place, but switching tabs to the Console and back will make the content appear at the bottom again.
1. Move the "Console" viewpart anywhere else from where it is
1. Click "Reset Layout" again
1. Notice it is irretrievably gone

#### Acceptance Criteria:
- Make "reset layout" reset partstacks containing shared elements to their original state and position in the layout