feat: Add additional scan time options

- Add option to include file existence check at end of scan, speeds up
  end of scan operation time considerably, however if user has removed
  or moved files since starting a scan there could be later errors when
  interacting with results.  Defaults to existing behavior of including
  the check, until it can be verified later dialogs and actions handle
  non-existent items better.
- Add option to ignore differences in mtime when checking hash cache.
  Option is present in advanced tab of preferences.  Closes #1022.
- Regenerate pot files for translations

locale/ui.pot

@@ -1092,3 +1092,17 @@ msgstr ""
 #: qt\search_edit.py:78
 msgid "Search..."
 msgstr ""
+
+#: qt\preferences_dialog.py:219
+msgid ""
+"These options are for advanced users or for very specific situations, most "
+"users should not have to modify these."
+msgstr ""
+
+#: qt\preferences_dialog.py:225
+msgid "Include existence check after scan completion"
+msgstr ""
+
+#: qt\preferences_dialog.py:227
+msgid "Ignore difference in mtime when loading cached digests"
+msgstr ""