Downloads and Other Updates

1. Added CanCan authorization for both collection downloads and single
raw file downloads.  Users must have at least read access to download.

2. Metadata added to downloads, now outputs both the metadata key as
well as the value (was just value).

Signed-off-by: shanesuofi <shanes@vandals.uidaho.edu>
Merge branch 'master' of https://github.com/cblair/portal into integration