New : add salaries in unpaid element manual reconciliation

I saw that the module was almost ready to work with salaries in the unpaid elements. I just added whats was missing and tested it on my side, it's working for me. My use case is that I create all my salary cards for each employee, and I have on my banking records 1 debit of the sum of it all. With this addition, I am able to link this debit to the N salaries.