Open links in current tab

Fix for #676

It removes the target of the link, as to prevent the website to overrule
the user. I guess the following things should be done:
 - add setting to enable/disable this behaviour
 - and/or add "hint all current"

Only the first one would be easiest. The second one requires us to keep track
of the original target. I should open a pull request for discussion.

qutebrowser/browser/hints.py

@@ -463,6 +463,7 @@ class HintManager(QObject):
                 QMouseEvent(QEvent.MouseButtonRelease, pos, Qt.LeftButton,
                             Qt.NoButton, modifiers),
             ]
+        elem.remove_target()
         for evt in events:
             self.mouse_event.emit(evt)
         if elem.is_text_input() and elem.is_editable():

qutebrowser/browser/webelem.py

@@ -285,6 +285,13 @@ class WebElementWrapper(collections.abc.MutableMapping):
         tag = self._elem.tagName().lower()
         return self.get('role', None) in roles or tag in ('input', 'textarea')
 
+    def remove_target(self):
+        """Remove target from link"""
+        if self._elem.tagName().lower() == 'a':
+            self._elem.removeAttribute('target')
+        elif self.parent().tagName().lower() == 'a':
+            self.parent().removeAttribute('target')
+
     def debug_text(self):
         """Get a text based on an element suitable for debug output."""
         self._check_vanished()