Konqueror web shortcut: better configurability of replacement strings.

See #5424-2: Konqueror: web shortcut.

Opening konqueror with the shortcut search string "git stash" leads to "git+stash" where "git_stash" is needed. I can certainly improve things within this site, but I do not control every site out there, and in the past I have met occasions where similar incompatibilities existed, where I wished konqueror didn't separate keywords with a + sign. For some sites, I may want a space, or an underscore instead, depending on what the target web site accepts.