Refactor Equation to be treated as a model and update Key Graph Features

[joseartrivera]

Part of #338.

Description of the changes:

The current way we transfer data from the EquationViewModel -> Equation is through duplicated dependency properties that are connected via two-way bindings in xaml. This is because the GraphControl was initially designed to receive a DataTemplate where the Equation FrameworkElement was supposed to be used. This isn't an ideal design since a DataTemplate should be able to accept any type of UI but currently would only work when used with the Equation FrameworkElement.

This PR refactors the code so that the GraphControl works more like the MapControl and the MapRouteView class. The GraphControl has a collection of Equations. To add an Equation to the Graph, we would append the equation to that collection and then call the PlotGraph() function.

This PR also updated Key Graph Features to use the new refactored way of transferring data. It was also updated to analyze an equation when the user clicks the button instead of analyzing them all at once.

How changes were validated:

• Manual tests

[sanderl]

    InspectingDataSource ^ m_dataSource;

You can remove this

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Refers to: src/GraphControl/Control/Grapher.h:206 in f242cd4. [](commit_id = f242cd4, deletion_comment = False)

[sanderl]

#include "InspectingDataSource.h"

This too

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Refers to: src/GraphControl/Control/Grapher.h:6 in f242cd4. [](commit_id = f242cd4, deletion_comment = False)