Capture the current state of xrviz for reuse

[rsignell-usgs]

We can currently specify the state of the GUI to xrviz, but we also should add the ability to capture the current state of xrviz for reuse.

[hdsingh]

This would require capturing the:

• zoom level
• location where it has been zoomed
• location of taps (in case user is extracting time series)

Please add here what else you think would be important to capture the state.

[martindurant]

Start without zoom/pan information. The location of taps is already known to the interface, and it is a good idea to be able to save and provide these.