Created a pdf class that takes care of the pdf wrapping

ref #3

src/controllers/PdfController.ts

@@ -15,6 +15,6 @@ export class PdfController {
     async generateContracts() {
         //TODO: Accept the real classes
         const contracts = await this.pdf.generateSponsoringContract();
-        return await this.pdf.toBuffer(contracts);
+        return await contracts.toBuffer();
     }
 }