Bug 20081: Set inline headers for uploaded pdfs

Bug 20081: Set inline headers for uploaded pdfs

To test:
1 - Edit a framework and add the 'upload/pl' plugin to the 856 field
2 - Attach a pdf to one record
3 - Attach a different type of file to another
(To attach, edit a record in the framework edited above and find the
 helper by the 856 field)
4 - Click the links on the record
5 - Verify the pdf opens inline
6 - Verify the other file does not
7 - prove t/db_dependent/Upload.t

Signed-off-by: Claire Gravely <claire.gravely@bsz-bw.de>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>