Fix bug that UI object elements getting part of export

Problem is that CubeViz modifies the objects itself while
building the user interface. Thats not a problem except
if you use these objects for the export functionality.

So adding the __cv_ prefix prevent the export function
to use these elements and keeps the exported file clean.
Fix bug: In case of switching datasets new array functionality strikes

Means, that in some way the comment is an array, whatever.
Just check before use string functions, otherwise leave
comment field blank.