Fixes for issue #206 (BetterUndoRedo)

[gotmachine]

We need to move calls to EditorLogic.SetBackup() before the actions take place (instead of after), see issue #206

• [x] Offset/Rotate gizmo The backup is created from callbacks called from the gizmo components OnMoveEnd / OnRotateEnd methods, triggered when the gizmo is released. The gizmos do have a On*Start method, but unfortunately they aren't hooked to a callback, and those are generic components that can potentially be used elsewhere. We can still patch those methods, and compare the gizmo instance to the EditorLogic.gizmo* fields.
• [x] Switching between part variants ~Requires moving the SetBackup() call at the beginning of the ModulePartVariants.onVariantChanged method~ Doesn't work because the field is already set when ModulePartVariants.onVariantChanged, so the changes will be saved to the backup anyway. Alternatively, we patch UIPartActionVariantSelector.SelectVariant()
• [x] Removing parts from symmetry Requires moving the SetBackup() call at the beginning of the Part.RemoveFromSymmetry method
• [x] Adding/removing part actions to action groups, and resetting part actions on the selected part Requires moving the SetBackup() call at the beginning of the EditorActionGroups ResetPart, AddActionToGroup and RemoveActionFromGroup methods
• [x] Using the reset button of the stage manager ~Requires moving the SetBackup() call at the beginning of the StageManager.Reset method~ Actually after further testing, it seems the backup is already created before the action, so nothing to fix here

[gotmachine]

Reverted to draft, as I forgot that we need to keep the firing of the GameEvents.onEditorShipModified from SetBackup() at the original point (ie, after the action took place). So more work is needed on those patches...

[gotmachine]

@JonnyOThan feel free to merge and push to a release