Make version upgrade also translate file names

This was required since Cura 2.1 produced files with the same filename (bar extension). This then resulted in two containers with the same ID. If you had bad luck, an instance container was chosen as global container (depending on which was first in the unordered dictionary). This gives the current settings the postfix _current_settings, fixing that issue.

Contributes to issue CURA-844.

plugins/VersionUpgrade/VersionUpgrade21to22/Preferences.py

@@ -10,11 +10,12 @@ import UM.VersionUpgrade #To indicate that a file is of the wrong format.
 #   in version 1 of the file format.
 #
 #   \param serialised The serialised form of a preferences file in version 1.
+#   \param filename The supposed filename of the preferences file.
 #   \return A representation of those preferences, or None if the file format is
 #   incorrect.
-def importFrom(serialised):
+def importFrom(serialised, filename):
     try:
-        return Preferences(serialised)
+        return Preferences(serialised, filename)
     except (configparser.Error, UM.VersionUpgrade.FormatException, UM.VersionUpgrade.InvalidVersionException):
         return None
 
@@ -24,7 +25,10 @@ class Preferences:
     ##  Reads version 2 of the preferences file format, storing it in memory.
     #
     #   \param serialised A serialised version 2 preferences file.
-    def __init__(self, serialised):
+    #   \param filename The supposed filename of the preferences file.
+    def __init__(self, serialised, filename):
+        self._filename = filename
+
         self._config = configparser.ConfigParser(interpolation = None)
         self._config.read_string(serialised)
 
@@ -42,7 +46,8 @@ class Preferences:
     #
     #   This is where the actual translation happens.
     #
-    #   \return A serialised version of a preferences file in version 3.
+    #   \return A tuple containing the new filename and a serialised version of
+    #   a preferences file in version 3.
     def export(self):
         #Reset the cura/categories_expanded property since it works differently now.
         if self._config.has_section("cura") and self._config.has_option("cura", "categories_expanded"):
@@ -70,4 +75,4 @@ class Preferences:
         #Output the result as a string.
         output = io.StringIO()
         self._config.write(output)
-        return output.getvalue()
+        return self._filename, output.getvalue()