Via db migrations, replaces the simple integer `reminder_day` with the more complex
`reminder_schedule` which is an ical string that can be parsed to a repeating Schedule class.
Adjusts the logic in the `fetch_partners_to_reminder_now_service` to use the repeating schedule.
Updates related tests.

Builds an ActiveModel, ReminderSchedule, which takes the necessary information
and turns it into an IceCubeSchedule, which is what ultimate get saved in the db.

Builds the form for this reminder schedule. Still needs to conditionally show or hide
sections depending on if the user wants date or day of the week.

Now either while creating new Organization/Partner Groups or editing them,
all the transfers from Reminder Date to Reminder Day have been made.

This uses css for ease and accessibility.

 Adds a number of refactors, including moving all the create_schedule logic
 to the deadlinable helper, and creates unit and system tests for the new functionality.

Reintroduces the functionality of having warnings for having the reminder
date the same as the deadline date.

…r-date-possibilities

We don't want to create a new schedule if nothing has changed,
as it will reset the start date and potentially mess with those
who have every 2/3/etc months reminders.

…into 4473-expand-reminder-date-possibilities

All reminders should be Monthly, so every N Months is removed.

Also allows users to select "Last" as an option.

Rather than "date" and "week_day", we are now using "day_of_month" and
"day_of_week" for clarity.

…r-date-possibilities

There was a bug in which if the reminder day of the month was the same
as the deadline day, it would dislplay the error message even if the user
changed to the day of the week option. Now the error message is hidden if
the user is selecting the day of the week option.