Also set Fusion style for downloads and completion

This makes those UI elements look the same on different platforms/OS styles,
with the small drawback of overriding the context menu style.

This most likely fixes #80 (though I couldn't reproduce that on Windows 10).

qutebrowser/browser/downloadview.py

@@ -23,7 +23,7 @@ import functools
 
 import sip
 from PyQt5.QtCore import pyqtSlot, QSize, Qt, QTimer
-from PyQt5.QtWidgets import QListView, QSizePolicy, QMenu
+from PyQt5.QtWidgets import QListView, QSizePolicy, QMenu, QStyleFactory
 
 from qutebrowser.browser import downloads
 from qutebrowser.config import style
@@ -75,6 +75,7 @@ class DownloadView(QListView):
 
     def __init__(self, win_id, parent=None):
         super().__init__(parent)
+        self.setStyle(QStyleFactory.create('Fusion'))
         style.set_register_stylesheet(self)
         self.setResizeMode(QListView.Adjust)
         self.setVerticalScrollBarPolicy(Qt.ScrollBarAlwaysOff)

qutebrowser/completion/completionwidget.py

@@ -23,7 +23,7 @@ Defines a CompletionView which uses CompletionFiterModel and CompletionModel
 subclasses to provide completions.
 """
 
-from PyQt5.QtWidgets import QStyle, QTreeView, QSizePolicy
+from PyQt5.QtWidgets import QStyle, QTreeView, QSizePolicy, QStyleFactory
 from PyQt5.QtCore import pyqtSlot, pyqtSignal, Qt, QItemSelectionModel, QSize
 
 from qutebrowser.config import config, style
@@ -117,6 +117,7 @@ class CompletionView(QTreeView):
 
         self._delegate = completiondelegate.CompletionItemDelegate(self)
         self.setItemDelegate(self._delegate)
+        self.setStyle(QStyleFactory.create('Fusion'))
         style.set_register_stylesheet(self)
         self.setSizePolicy(QSizePolicy.Expanding, QSizePolicy.Fixed)
         self.setHeaderHidden(True)