Add possibility to let a user choose from already uploaded images

[Uatschitchun]

When adding a Projekt or Veranstaltung, the user is able to add image(s). Sadly it's only possible to choose from images uploaded to the post.
It would be nice if a user is able to choose from images her/she has already uploaded before or on other posts (Projekte, Veranstaltungen, etc. So a per user gallery for images instead of a per post gallery to choose from.
This would minimize (disk-)space usage and redundant images being uploaded more than once.