fractal-gtk: Use gspell for spellchecking
With the move to GtkSourceView, we no longer had spellcheck support in Fractal as bindings for GspellTextView were not generated.
Related to https://gitlab.gnome.org/GNOME/fractal/issues/124
With the move to GtkSourceView, we no longer had spellcheck support in Fractal as bindings for GspellTextView were not generated.
Related to https://gitlab.gnome.org/GNOME/fractal/issues/124