Removed SwissPaymentSlipData and SwissPaymentSlip classes and its associated files (moved them to a separate repo)
Added the newly creates swiss-payment-slip/swiss-payment-slip package as a dependency
In preparation
 1. To move SwissPaymentSlipPdf also to a separate repo
2. dividing FPDF implementation from TCPDF (by cloning the class)
and
3. to move those implementations into a repo of their own