ignore immediate=True in progress dialog

Instead, set the busy cursor immediately to give the user feedback,
but defer popup for at least 500ms. This will hopefully address the
white flash in night mode on Windows, and prevent progress dialogs
from rapidly appearing and disappearing for short operations.

qt/aqt/progress.py

@@ -106,6 +106,7 @@ class ProgressManager:
                 evt.ignore()
                 self.wantCancel = True
 
+    # note: immediate is no longer used
     def start(self, max=0, min=0, label=None, parent=None, immediate=False):
         self._levels += 1
         if self._levels > 1:
@@ -124,10 +125,8 @@ class ProgressManager:
         self._win.setWindowTitle("Anki")
         self._win.setWindowModality(Qt.ApplicationModal)
         self._win.setMinimumWidth(300)
-        if immediate:
-            self._showWin()
-        else:
-            self._shown = False
+        self._setBusy()
+        self._shown = False
         self._counter = min
         self._min = min
         self._max = max
@@ -159,8 +158,10 @@ class ProgressManager:
     def finish(self):
         self._levels -= 1
         self._levels = max(0, self._levels)
-        if self._levels == 0 and self._win:
-            self._closeWin()
+        if self._levels == 0:
+            if self._win:
+                self._closeWin()
+            self._unsetBusy()
 
     def clear(self):
         "Restore the interface after an error."
@@ -181,7 +182,6 @@ class ProgressManager:
     def _showWin(self):
         self._shown = time.time()
         self._win.show()
-        self._setBusy()
 
     def _closeWin(self):
         if self._shown:
@@ -197,7 +197,6 @@ class ProgressManager:
         self._win.cancel()
         self._win = None
         self._shown = False
-        self._unsetBusy()
 
     def _setBusy(self):
         self.mw.app.setOverrideCursor(QCursor(Qt.WaitCursor))