Add new buttons for Sandcastle-Camera

[SambaLim]

Hello, We added the features cancleFlight and completeFlight to the Camera, but we haven't been able to test it on the Sandcastle Camera. Therefore, I added buttons to test this through Sandcastle.addToolbarButton.

What do you think of adding it like this?

[cesium-concierge]

Thanks for the pull request @SambaLim!

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[IanLilleyT]

Thanks for adding these @SambaLim

I had to refactor the sandcastle to not use Sandcastle.reset since the Complete Flight and Cancel Flight buttons were triggering Sandcastle.reset and causing primitives and events to be removed.

[SambaLim]

Thanks @IanLilleyT

I am very happy with the contribution to Cesium.js