Main: Initialize WidgetsBinding before running the app.

[kwight]

This PR ensures a WidgetsBinding instance is initialized before running the app.

If this instance is not initialized before our loadData() call, the app will fail to compile with an unhandled exception: "ServicesBinding.defaultBinaryMessenger was accessed before the binding was initialized."

Testing Instructions

• Check out this repo and attempt to start the app.
• Notice it will fail to start, breaking on the unhandled exception given above.
• Switch to this PR.
• Restart the app, and verify it loads correctly.