Issue 935 - Updates to Scientific/Graphing Keypad (#1214)

* Switching from Difference between dates to Add or subtract dates ignores the first date field

https://github.com/microsoft/calculator/issues/254

Date field needs to persist across Date Difference and Add/Subtract From Date Mode.

* Update DateCalculator.xaml.cpp

Addressing review comments (white space, small code refactor), also found a null pointer exception during testing, this fix addresses that as well.

* Issue 935 - Updates to Scientific/Graphing Keypad

Update Scientific and Graphing keyboard layouts to expose square root button at the top level

* Updated ScientificModeFunctionalTests/SmokeTest_Cube()

Updated broken test to work with changes.

src/CalculatorUITests/ScientificModeFunctionalTests.cs

@@ -69,6 +69,7 @@ namespace CalculatorUITests
         public void SmokeTest_Cube()
         {
             page.StandardOperators.NumberPad.Input(3);
+            page.ScientificOperators.ShiftButton.Click();
             page.ScientificOperators.XPower3Button.Click();
             page.StandardOperators.EqualButton.Click();
             Assert.AreEqual("27", page.CalculatorResults.GetCalculatorResultText());