Toolbar in Fixed Position (#2194)

* Initial attempt at getting the toolbar for the fixed position working with the Vue toolbar controls.

* Set title for controls

* Significant mods to support legacy Fixed Position

- Moved selection and editing styles into _global.scss;
- Changed class naming in legacy fixed.html to map to newer CSS styles;

* Pass in the color value

* Do not show the toolbar container if structure is empty.

* Use a plugin for fixed position to get access to openmct. Show the toolbar only if the object is being edited.

* Ensure fixedController is on the selection context when editing

* Add listener for a domain object with the same id only once.
Update the toolbar value after the object mutation.
Remove editor isEditing listener on destroyed.

* Remove space between the size and px.
If newObject exists, update the toolbar value.

* Remove --nwse class name which seems to be a typo

* use modifier convention

src/plugins/displayLayout/plugin.js

@@ -72,6 +72,7 @@ export default function () {
                 // and in edit mode.
                 return (selection &&
                     selection[1] &&
+                    selection[1].context.item &&
                     selection[1].context.item.type === 'layout' &&
                     openmct.editor.isEditing());
             },