Equation button updates: Enable/Disable on click, button content f1, f2, f3..., visibility icon on hover (#804)

* Added enable/disable line functionality

* Update EquationTextBox to change the opacity of functions have are not visible. Update the function label for the EquationTextBox to increment the label to show f1, f2, f3, etc

* rebase key-graph-features and fix issue where removing an equation box and adding a new one repopulates the previous equation

* Added visibility icon for the equation button hover

* updated EquationButton to be a toggle button to better handle the LineHidden state and other PR comment fixes.

* Updated EquationButton style to use a toggle button and to have placeholder icons for the show/hide states

* Updated equation button after pulling the refactor work into the branch. Fixed the Equation Button in KGF UI

* Fixed Pepe's bugs

* Uncomment temporary.pfx in calculator.vcxproj

src/Calculator/Views/GraphingCalculator/KeyGraphFeaturesPanel.xaml.h

@@ -18,7 +18,6 @@ public
 
         OBSERVABLE_OBJECT_CALLBACK(OnPropertyChanged);
         OBSERVABLE_PROPERTY_RW_ALWAYS_NOTIFY(CalculatorApp::ViewModel::EquationViewModel ^, ViewModel);
-
         event Windows::UI::Xaml::RoutedEventHandler ^ KeyGraphFeaturesClosed;
 
     private: