update readme
add public activity gem

See https://github.com/pokonski/public_activity
add `Trackable`

to track activity on models
add `ControllerTrackable`

and tracking clientes’ activity
add `skylight` on production
refactor `SaniGetWorker` and `SaniPostWorker`

to inherit from `SaniWorker`
Merge branch 'master' into heroku