Package browser list icon placeholders

[Informatic]

Enyo has a notion of image placeholders, but that's incompatible with images with transparency (it's set as a background-image of a wrapper on an image) so that the placeholder leaks through the icons.

It'd be great to get some placeholder in case of missing/broken icons.

We could also potentially add iconColor attribute to package manifest, equivalent to the one used on homescreen, to make the rendering more familiar. A random thought.

[Informatic]

ref: http://latest.enyojs.com/sampler/dist/enyo/index.html#ImageSample (for source code: View source → enyo-samples.js → Ctrl-f → ImageSample 🙃)