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 branch '633-fix_download_of_external_files' into develop
use to_s on entity instead of explicit call.
always replace _ with whitespace for display name.
Merge branch '725-entity_display_name_issue' into develop
introduce the new mirror icon
Merge branch '573-mark_mirrored_repositories' into develop
Merge branch 'develop' into develop.ontohub.org