feat: add javascriptFile property (The same as styleSheetFile property but for js files)

[thederickff]

Hello, I am using ngx-print with Ionic+Angular, and I figured out that the <ion-icon></ion-icon> element was not being rendered, because of the missing ionicons's javascript file: <script src="https://unpkg.com/[email protected]/dist/ionicons.js"></script> Therefore, I decided to add the possibility for users being able to add scripts to the printing window page just like it is possible to do with the stylesheets. I really need these icons on my prints, but I don't know for sure yet how can I get this new version of 'ngx-print' into my project, I'll be waiting for your response.

[thederickff]

Hello, I would really appreciate if you could add this functionality. You don't even need to merge it, you could add it into the project by yourself.