add uri fetcher to fetch corresponding files

we can either fetch them to memory or directly
to the harddrive.
use uri-fetcher for the external repository.
Merge branch 'staging' into 633-fix_download_of_external_files
fix namespacing and method-name for uri-fetcher.
fix module inclusion and param for downloading.
adjust external-repository fileadd for location.
move filedownload for external repository

The file download step for the external repository
needs to be moved into the 'reference' node proc,
in order to handle its location attribute.
Merge pull request #730 from ontohub/633-fix_download_of_external_files

Follow redirects on download of external files. Fixes #633.