Trait days, add new days and remove't, just like load initial days
Receive a list of string with days and create event_days.

When update, remove all and insert new days. Also return a list of days
like string array.
Receive event_days param, and create or update this
Presence true of day in event_day
Use helper to show attribute of event
Change icon when focus in 'x' ico or 'calendar' ico
Remove default values from tags