Mouse gestures

Hi,

Jan-Michael added experimental support for Opera-style mouse gestures 
using the middle mouse button in Epiphany 3.31.4. You can enable it 
using /org/gnome/epiphany/web enable-mouse-gestures in dconf-editor. 
See https://gitlab.gnome.org/GNOME/epiphany/merge_requests/113 for 
details.

I had been hoping it would use the right mouse button, to copy Opera 
and potentially avoid the need to add extra settings like "what button 
should control the gestures?" (and, god forbid, "what particular 
gestures should be enabled?") by sticking to Opera's defaults. Alas, 
right mouse button ran into a snag. This works on other platforms where 
context menus are opened on mouse button release, but GTK+ apps open 
context menus on button press. So if we want to use right mouse button, 
we are going to have to switch to opening context menus on button 
release instead of button press. (Otherwise, a context menu would be 
opened at the start of every gesture.) It should be possible, but a bit 
hacky.

I wonder how many people are interested in mouse gestures, and if 
restricting them to middle mouse button would be OK? Middle button 
seems totally fine once you get used to it, but I fear diverging from 
expected behavior in other browsers.

Michael