[Dillo-dev] Key binding for viewing page source

Alexander wrote:

I use the "view page source" function from the right-click popup menu very often and so I created a key binding for this (see attached patch). Since I find this very handy, please consider this patch for the repository.

This would be good to have. I was thinking that the key check might fit more naturally in UI::handle() rather than CustTabs::handle(), but I see that ui.cc doesn't currently know anything about nav or history, so now I'm not sure...