Add Icon and backdrop in .dext package

[sanket143]

Note: This issue is reserved for SLoP Contributors.

When packaging using sinix pack, check if sinix.config.js of the project which is using sinix.js contains a path
to icon and backdrop path. If it does add it in the generated .dext.

for sinix.config.js

module.exports = {
  title: "Sinix App",
  distDir: "public/",
  iconSrc: "images/icon.png",
  backdropSrc: "images/wallpapers/01.jpg"
}

following should be the path of icon and backdrop in the .dext pack.

for icon: .sinix/images/icon.png
for backdrop: .sinix/images/wallpapers/01.jpg

and sinix.manifest.json

{
  ...
  "icon": ".sinix/images/icon.png",
  "backdrop": .sinix/images/wallpapers/01.jpg
}