In addition to the existing "Remove" menu action in the Image Gallery that
deletes the currently selected image, add a "Remove All Images" menu
action that performs the same action as "Clear Images" from the "File"
menu.

The "Del" key was used as a shortcut to remove the currently selected
image when the Image Gallery has the focus, "Shift+Del" can now also be
used to remove all the images at once.

Update the names of the commands that remove images in the "File"
menu to match with those in the Image Gallery menu.

"Clear Images" becomes "Remove All Images" and "Clear All Images" becomes
"Remove Images From All CameraInit Nodes".