Keep a reference to ContentPage's internal GtkGrid
Keep a reference to ContentPage's internal GtkGrid

We need to keep this around because it's referenced in the key press
handler for Ctrl+F.
[endlessm/eos-sdk#3435]

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