Creating a shortcut to a listing of a specific content type or a set of specific nodes I want to create a shortcut that acts similar as when you click the "Content" link. But I want to be able to display only a specific content-type or probably a specific set of nodes.

Is this possible weather by coding or through a module?
You can do it with the Views module and some additional extensions.

The easiest way to do it is to install the Administration Views module (and all of its dependencies). It provides administrative lists just like you get from Drupal core, except they're built using Views.

Once you have that installed, go to /admin/structure/views. Clone the "Administration: Nodes" view provided by Administration Views, change the node type filter to be fixed instead of exposed, change the system path setting (eg. /admin/content/my-node-type) and save it.

That should be all - let me know if I messed a step or if something is unclear.