Genericize implementing views which expose common attributes
Summary: Some views expose some/most/all of the basics (id, class, sigil, metadata, etc); let them extend a dedicated view to get it for free.
Test Plan: Viewed home page, paste, mobile dropdown, etc.
Reviewers: btrahan, chad
Reviewed By: btrahan
CC: aran
Differential Revision: https://secure.phabricator.com/D4440