Removed 'choose_from_most_used' from category

Categories are hierarchical, `'choose_from_most_used'` is only used for non-hierarchical taxonomies. :)
Merge pull request #2809 from vlandfair/patch-1

Removed 'choose_from_most_used' from category
Make sure $download_list is defined before concatenating strings.
Merge pull request #2816 from dannyvankooten/fix/undefined-var-download-list

Make sure $download_list is defined before concatenating strings.
Add @cklosowski to contributors list. How had this not been done before?
Merge branch 'master' into release/2.2