@Nebel54 I have updated the code and have added render array. Now the the cart will be fully rendered using the template file, earlier the table was rendered in the preprocess function, which is not a good approach. Now the template file will handle the rendering process. The preprocess function only adds additional values for rendering. @Nebel54 could you please the latest dev version of the code.
The teaser block and add to cart message templates are alright, therefore I am marking this issue as "Fixed". Please feel free to re-open if you face any problem.
Although this is a major change in module, but I am not releasing it in 2.x branch because it is just a change in rendering process, there is no major change in the implementation of the module.
@discipolo Please create a new issue for the view mode, we will discuss it over there.
@Nebel54++ thanks for raising this issue :)