Clear WebEngine's HTTP cache on start-up

I noticed that after replacing the JavaScript bundle, WebEngine continues
to use parts of the old code. Clearing the cache fixes this, though it is
a bit heavy-handed.

spyder_notebook/utils/servermanager.py

@@ -16,6 +16,7 @@
 
 # Qt imports
 from qtpy.QtCore import QObject, QProcess, QProcessEnvironment, QTimer, Signal
+from qtpy.QtWebEngineWidgets import QWebEngineProfile
 
 # Third-party imports
 from jupyter_core.paths import jupyter_runtime_dir
@@ -123,6 +124,10 @@ def __init__(self, dark_theme=False):
  """
  Construct a ServerManager.
 
+ This constructor also clears Qt WebEngine's HTTP cache, because for
+ unknown reasons WebEngine seems to use out-of-date code after the
+ JavaScript bundle is replaced.
+
  Parameters
  ----------
  dark_theme : bool, optional
@@ -132,6 +137,7 @@ def __init__(self, dark_theme=False):
  super().__init__()
  self.dark_theme = dark_theme
  self.servers = []
+ QWebEngineProfile.defaultProfile().clearHttpCache()
 
  def get_server(self, filename, interpreter, start=True):
  """