Fix static method
Force UTC zone for `sendCacheControlHeaders` dates
Model addtions for scheduled items
Re-generate model with changes
Implement scheduler backend.

Entries in scheduled actions can be polled and executed.
Implement “activate” action for pages
add filter for scheduled/unscheduled
make sure to use UTC for execution date
add scheduler icon
Add scheduler widgets
Add scheduler widget to page detail

FIXME: Find better place
Use timezone_input for scheduler widget
Use server time zone instead of UTC explicitly

Since the server time zone is UTC, this should not matter.
But should it ever be some other zone, it’ll still work.
Add shell script to process scheduled actions
generate model