Change key to leave passthrough mode to Shift-Escape

We changed this a while ago in a2f62238f1
already, but Ctrl-V was kind of cumbersome as well, as it conflicted with
pasting.

Shift-Escape is closer to the default leave-mode binding (Escape), and also
unlikely to conflict as it's used for the task manager in Chrome.

doc/changelog.asciidoc

@@ -30,6 +30,9 @@ Changed
 
 - The `:repeat` command now takes a count which is multiplied with the given
   "times" argument.
+- The default keybinding to leave passthrough mode was changed from `<Ctrl-V>`
+  to `<Shift-Escape>`, which makes pasting from the clipboard easier in
+  passthrough mode and is also unlikely to conflict with webpage bindings.
 
 v1.4.2 (unreleased)
 -------------------

doc/help/settings.asciidoc

@@ -634,7 +634,7 @@ Default:
 * +pass:[}}]+: +pass:[navigate next -t]+
 - +pass:[passthrough]+:
 
-* +pass:[<Ctrl-V>]+: +pass:[leave-mode]+
+* +pass:[<Shift-Escape>]+: +pass:[leave-mode]+
 - +pass:[prompt]+:
 
 * +pass:[<Alt-B>]+: +pass:[rl-backward-word]+

qutebrowser/config/configdata.yml

@@ -2481,7 +2481,7 @@ bindings.default:
       <Ctrl-B>: hint all tab-bg
       <Escape>: leave-mode
     passthrough:
-      <Ctrl-V>: leave-mode
+      <Shift-Escape>: leave-mode
     command:
       <Ctrl-P>: command-history-prev
       <Ctrl-N>: command-history-next