Fix some bugs

- Rename parameter to avoid break database updating.
    Parameter RETURN_MONEY_ON_SALES was modified in stoqlib.lib.parameters
    to RETURN_POLICY_ON_SALES, but not renamed in database.
- Fix Calendar app when start.
- Fix translation.

Change-Id: Ibd42bb4b798c42237246df4d466e33aed95a68b2