Automatic creation of fiscal year sequences.

    This module adds the possibility to use the `%(fy)s` placeholder
    in sequences. `%(fy)s` is replaced by the fiscal year code when
    using the sequence.

    The first time the sequence is used for a given fiscal year,
    a specific fiscal year sequence starting at 1 is created automatically.

    /!\ If you change `%(year)s` to `%(fy)s` on a sequence that has
    already been used for the current fiscal year, make sure to manually
    create the fiscal year sequence for the current fiscal year and
    initialize it's next number to the correct value.
    For this reason, the module will forbid the user to change
    a sequence from `%(year)s` to `%(fy)s` if it's next number is > 1.

    The module also replaces `%(year)s` by `%(fy)s` in the default prefix
    for new journals, assuming it is a safer default.