fix(e2e): openNthCalculator() : select option naming does not always start at 0

refs #592

e2e/navbar.po.ts

@@ -31,8 +31,11 @@ export class Navbar {
         const dropDown = element(by.css("mat-select#selectCalculator"));
         if (await dropDown.isPresent() && await dropDown.isDisplayed()) {
             await dropDown.click();
-            const optionId = ".cdk-overlay-container mat-option#mat-option-" + n;
-            const option = element(by.css(optionId));
+
+            // 1st option is not necessarly "mat-option-0"...
+            const options = element.all(by.css(".cdk-overlay-container mat-option"));
+            const option = options.get(n);
+
             await option.click();
         } else {
             const tabs = this.getAllCalculatorTabs();