Preview diploma thesis

[mkhumml]

As a teacher I want to have a preview of the diploma thesis so that I don't have to download it every time.

Acceptance criterias:

• It should be possible to preview the .pdf files in the browser without having to download them
• There should be a "preview" button beside every diploma thesis
• If the button is clicked the diploma thesis .pdf should open up in the browser
  • If the button is clicked but there is no .pdf of the diploma thesis, there should be an error message
• To leave the preview, there should be a "leave preview" button
• If the "leave preview" button is clicked, you should get back to the diploma thesis table

[sebastian15038]

It is possible to output diploma thesis and click on the attachments. They will open in the browsers. Finished, There is no preview button but the links are marked. There is no leave preview button because this case will be done by the browser