V2.0.1 upgrade wizard

This was based upon the work done by Norbert, with the following changes:

- Externalized message strings for capability of translation
- Fixed a manual upgrade issue mentioned in issue 1580.
- Changed the importing behaviour a bit so that the Add/Replace doesn't appear in the following two cases:
a) Shared decks. They are always added and no import dialog appears to the user.
b) Importing during the upgrade wizard. This does replacing. A dialog appears to let the user decide which .apkg file has their collection.

- Cleaned up the shared deck tmp file, after the download finishes. This was left over before in AnkiDroid folder and is an .apkg, so it would appear as available for import when doing re-upgrade, or simple "Import cards".