Properly remove old lightbox content when setting new content
Properly remove old lightbox content when setting new content

At some point we moved to LightboxContainer containing its a grid
for its widgets rather than widgets being a direct child. But we
were still making a call to LightboxContainer.remove expecting it
to remove the grand child widget. Call remove on the internal grid
instead
[endlessm/eos-sdk#1617]

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib