Use OcResource component for filename in pdf-viewer

[kulmann]

The filename in the header section of the pdf-viewer app currently shows the plain text filename (see screenshot).

It could use a bit of eyecandy. Let's try if using the OcResource component, which automatically shows the file type icon as well, looks good. Would also serve as a small reminder to the user that the active app is the pdf viewer, as it would always show the pdf file type icon. ;-)