Image holder mixins

[popvasilevlad]

No description provided.

[robipop22]

@ionuttoader @radufarcas10 @per0xide @ileaugustin review this too pls

[radufarcas10]

I think we should find a way to keep examples separate from the features, to leave index.html untouched and only use it in development.
But until we figure out how to separate the examples from the core code, please checkout index.html when making commits, because we don't want all the examples to be in the root index.html, especially on branch integration

[radufarcas10]

remove the code from index.html