Added PDF embed

@NoahY: Feature added to embed PDFs. 

Details: 
- Get blob-URLs from the post, 
- check their filetype, 
- if pdf, append them in the end of the post as PDF-embed. 

Requires: 
- qa-blob.php edit to serve PDF-Blobs inline instead of attachment (probably solved with q2a v1.7)

Greetings,
Kai

Signed-off-by: q2apro.com <info@q2apro.com>