[ADD] 7.0 account_auto_fy_sequence

    Automatic creation of fiscal year sequences.

    This modules 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.

@pedrobaeza Well, that is surprising I know, but it is the way it is done in the super class
https://github.com/odoo/odoo/blob/8.0/addons/account/ir_sequence.py#L49

I think it is correct and works because fiscal year sequences only make sense in accounting were we have one possible sequence per journal, therefore len(seq_ids) == 1.