[Feature request] - Image Component with Preview image and srcset

**I'm submitting a ...** (check one with "x")

* [ ] bug report
* [x] feature request

I would recommend highly the implementation of a image component like i created here: https://github.com/DevMonkeysDE/ngx-mark6/tree/master/projects/mark6-lib/src/lib/image

The features are:

- can show preview image while the src is loading the real one. (I do directly in the object of a p post or user a 24x24px base64 image as string and use it as preview image. So when the item inside of a ngFor gets loaded users will see directly a preview low res image. That improves the UX alot! When the real image gets loaded i have a fade animation to switch the images. if src is not found people can define a fallback / error image.
- can define a aspect ratio. This makes alot sense in my eyes.
- srcset can be bound directly by nebular breakpoints. then people just need to pass a mobile, a tablet and a desktop image. Would be save alot of time to the people.

Please feel free to copy my image component and customize it.

At last replace and use this image component everywhere, where you guys use any image :)

You can btw see how it feel and look in my app: https://pixer.app/de/stories/new (its still in development and buggy in some aspects)