Webkit-gtk version

[Robert Fewell]

Just want to clarify what versions of webkit-gtk is now required. My test
VM that has gtk3.10 and webkit2gtk-4.0, version 2.6.6 which does not have
"allow-file-access-from-file-urls", 2.10 has this and so end up with error
in trace file and there is also a critical error when I close gnucash with
a report page open. My other test VM has gtk3.22 and webkit2gtk-4.0,
version 2.16.3 and so I do not see this problem.

I suppose if it tested for version 2.10 and was not found it could fallback
to webkit1gtk which I think is also installed.

Bob