Layout drawing (#2232)

* - Show "Add" button in the toolbar when a display layout object is selected.
- Add a flag to object view's show() method to indicate immediate selection of the view. If the view implements getSelectionContext() use it, otherwise set to default context.

* Create a component for each element.

* Saving work

* Add element factory for creating new instances of elements.

* Mutate element when a new one added and get elements when the component is mounted.

* Add create() method for creating a new telemetry and element in their respective view configuration.

* Add some of the toolbar controls for box, text, image and line elements. Also, add X, Y, Width and Height controls for alhpanumeric elements.

* Pass name to addElement as type.

* Add c-frame-inspectable class if item is inspectable.

* Clean up

* Hide frame for summary widgets by default.

* Better styling for editing

- s-selected on shell__main-container;
- Better edit grid coloring for espresso;

* - Update toolbar-button to support dialogs.
- Update toolbar to construct a value object based on form keys if a toolbar item has a dialogi, and mutate the form keys.
- Add toolbar controls for editing text and url for 'Text' and 'Image' elements respectively.

* Editing-related changes

- Removed hard-coded .is-selectable and .is-moveable from
LayoutItem.vue, updates accordingly to _global.scss;
- Theme constants updated;
- TODO: apply changes to Flexible Layouts;

* Better defaults

- Better default grid size and object size;

* - Fix toolbar-input to read value as a number if type is 'number'.
- Remove rawPosition from view configuration and instead get the position and dimensions from the properties (x, y, width and height) directly.
- Set the style property on the view configuration instead of the layout item.
- Move the logic for updating the style to the view configuration.

* Fix default dimensions for telemetry items and subobjects since the default grid size is changed.

* Remove form definition for display layout type.

* Reword the comment

* Let subobject view configuration handle new panel creation.

* Add default grid size back and remove unused code.

* Pass in only the needed method.

* Define default position in case the object is not added via drag 'n drop.

src/plugins/displayLayout/plugin.js

@@ -41,7 +41,7 @@ export default function () {
                             components: {
                                 Layout
                             },
-                            template: '<layout :domain-object="domainObject"></layout>',
+                            template: '<layout ref="displayLayout" :domain-object="domainObject"></layout>',
                             provide: {
                                 openmct,
                                 objectUtils
@@ -54,6 +54,12 @@ export default function () {
                             }
                         });
                     },
+                    getSelectionContext() {
+                        return {
+                            item: domainObject,
+                            addElement: component && component.$refs.displayLayout.addElement
+                        }
+                    },
                     destroy() {
                         component.$destroy();
                     }