Create button "Plot Different Key" which is disabled by default.
After data is loaded, if there are more than one key for the data, the button will be enabled.
User click on that to access a dialog that allow user to select a different key. Suppose that all data have been finalized right after loaded, we don't have to do finalized here but have to wait until !142 (merged) is merged
Then replot_loaded_data() will be call to replot the selected data.