Context-Menu for Tables (#2424)

* add context menu capability to table rows, add view switcher to preview

* add an option to limit context menu actions to the ones requested, and modify preview action to also include a view historical data action

* extend preview action into view historical data action

* add context menu to LAD Table

* add keys to context menu actions, allow tables to conditionally attach context menu handler

* working switch y axis label

* New vertical select element for Y axis configuration in plots

- CSS for vertically rotated selects for Y axis label selection;
- New theme constants;
- Removed themedSelect theme mixins;
- New SASS svgColorFromHex function;

* use keys in lad table context menu options

* show historical view context menu on alpha-numerics

* make reviewer requested changes

* pass contextual object path from object view down etc

* made reviewer requested changes: removed options object, pass in object path instead

* remove redundant function from LADRow.vue

src/plugins/remove/RemoveAction.js

@@ -23,6 +23,7 @@
 export default class RemoveAction {
     constructor(openmct) {
         this.name = 'Remove';
+        this.key = 'remove';
         this.description = 'Remove this object from its containing object.';
         this.cssClass = "icon-trash";