Selection in grid context (#2527)

* update action context on selection change

* correctly add ranges rather than a new range for every row

* add required functions to typings

src/typings/globals/slickgrid/index.d.ts

@@ -764,6 +764,16 @@ declare namespace Slick {
 		**/
 		destroy(): void;
 
+		/**
+		 * Sets selected ranges for the grid
+		 */
+		setSelectedRanges(ranges: Slick.Range[]);
+
+		/**
+		 * Gets selected ranges for the grid
+		 */
+		getSelectedRanges(): Slick.Range[];
+
 		onSelectedRangesChanged: Slick.Event<E>;
 	}