Fix progressbar height to statusbar height.

Formerly, the statusbar height changed when the progressbar was visible.
This was caused by the default font-size of the progressbar text (though
invisible). Overriding the minimumSizeHint() method ignores the
font-size of the hidden text and the statusbar height does not change
anymore.

This fixes the first issue of #886.

qutebrowser/mainwindow/statusbar/progress.py

@@ -79,5 +79,9 @@ class Progress(QProgressBar):
     def sizeHint(self):
         """Set the height to the text height plus some padding."""
         width = super().sizeHint().width()
-        height = self.fontMetrics().height() + 3
+        height = self.fontMetrics().height()
         return QSize(width, height)
+
+    def minimumSizeHint(self):
+        """Set the height to the text height plus some padding."""
+        return self.sizeHint()