Added not-null constraints to db columns.
Added refresh_feed_jobs_updated_at attribute to User model.

The new attribute will indicate when refresh feed jobs for the user were updated for the last time. It defaults to the current datetime if not set.
The refresh_feed_jobs_updated_at attribute of User instances is set to the current datetime when appropiate.
Added HTTP caching support to RefreshFeedJobStatesController#index action
Do not send a parameter with the current time when requesting refresh feed job states via Ajax.

It was keeping the client from leveraging HTTP caching.
Added HTTP caching support to RefreshFeedJobStatesController#show action
Do not send a paramter with the current time when requesting a refresh feed job state via Ajax.

It was keeping clients from leveraging HTTP caching.
Added subscribe_jobs_updated_at attribute to User model.

It will indicate when were subscribe job states last changed for this user.
The subscription_jobs_updated_at attribute of User instances is updated at the appropiate times.
Added HTTP caching support to SubscribeJobStatesController#show action
Added HTTP caching support to SubscribeJobStatesController#index action
Do not send a parameter with the current time when requesting for either individual or all subscribe job states via Ajax.

It was keeping clients from leveraging HTTP caching.
Added fragment caching to the views that return JSON for the hopscotch tours.