Add bindings for xo/xO (backtabopen(cur))

TODO

@@ -361,12 +361,6 @@ Show and execute userscripts (command execute_userscript).
 Other
 -----
 
-xo
-Open url in a new tab in background, the argument $URI will be repaced with the current uri (command: backopen, aliases: bopen ).
-
-xO
-Open url in a new tab in background, set current url in the navigation bar (command: backopen_url).
-
 wo
 Open url in a new instance (command: winopen, aliases: wopen, w).
 

qutebrowser/config/configdata.py

@@ -545,6 +545,8 @@ DATA = OrderedDict([
         ('go', 'opencur'),
         ('O', 'tabopen'),
         ('gO', 'tabopencur'),
+        ('xo', 'backtabopen'),
+        ('xO', 'backtabopencur'),
         ('ga', 'tabopen about:blank'),
         ('d', 'tabclose'),
         ('co', 'only'),

qutebrowser/widgets/_tabbedbrowser.py

@@ -282,6 +282,12 @@ class TabbedBrowser(TabWidget):
         url = urlutils.urlstring(self.currentWidget().url())
         message.set_cmd_text(':open ' + url)
 
+    @cmdutils.register(instance='mainwindow.tabs', hide=True)
+    def backtabopencur(self):
+        """Set the statusbar to :backtabopen and the current URL."""
+        url = urlutils.urlstring(self.currentWidget().url())
+        message.set_cmd_text(':backtabopen ' + url)
+
     @cmdutils.register(instance='mainwindow.tabs', name='undo')
     def undo_close(self):
         """Switch to the previous tab, or skip [count] tabs.