Load files into list, not dict to keep duplicate filenames

Load files into list, not dict to keep duplicate filenames

By loading all downloaded rule files into the same dict, filenames
that are the same cause other files to be lost, and the content
may be different.

Instead use of list objects that tracks the filename and the content
to avoid losing the contents of a filename that already exists.

If the contents is duplicated, the rule deduplication process
will catch that.

Redmine ticket:
https://redmine.openinfosecfoundation.org/issues/3174