Refactor: move common method #to_json_date to test_helper.rb
Use explicit jbuilder template to return v1 json
Implement v1 using v2 tables.

Point feed_items_controller at v2's item table instead of the
original v1's feed_item table.
Retire feed:refresh rake task, update desc on rss_loader:load task
Remove superfluous comment
Drop retired v1 table feed_items
Add Release note to README