Impacted versions:
10.0 + e

Steps to reproduce:
1) Create a salary rule that has 'appears_on_payslip' = False.
- An example would be a company contribution that the employee does not need to see.
  2) Add it to a salary structure
  3) run a payroll/payslip calculation

Current behavior:
Numerous thing.
1) Every time you compute sheet, you will duplicate these 'hidden' lines
2) details_by_salary_rule_category no longer has any of the hidden lines, though they certainly contribute to categories (e.g. tests will fail, and bad things)
3) when using hr_payroll_account, lines with contribution registers and accounts that SHOULD be on the journal entry are not !!

Expected behavior:
1) every time you compute the sheet, the lines should be deleted and recalculated
2) details_by_salary_rule_category should have all categories (to be able to make complex rules and tests)
3) journal entry should have a line for every line with an account

Pull Request eminent.

"""
    Employee contract based on the visa, work permits
    allows to configure different Salary structure
    """
    _inherit = 'hr.contract'
    _description = 'Employee Contract'
    struct_id = fields.Many2one('hr.payroll.structure', string='Salary Structure')
    schedule_pay = fields.Selection([
        ('monthly', 'Monthly'),
        ('quarterly', 'Quarterly'),
        ('semi-annually', 'Semi-annually'),
        ('annually', 'Annually'),
        ('weekly', 'Weekly'),
        ('bi-weekly', 'Bi-weekly'),
        ('bi-monthly', 'Bi-monthly'),
    ], string='Scheduled Pay', index=True, default='monthly')
    @api.multi
    def get_all_structures(self):
        """