Add "start_date" and "end_date" fields to AppSignups, set when the maker accepts

[ddgriffin]

The maker would hit the "Accept" button and get a popup asking them to set/update the start and end dates for this particular apprentice - we'll base our check-ins and support on these dates.

ALSO, lets change the x-edit date picker to a dropdown that has 1-day, 1-week, 1-month, 2, 3, 4, 5, 6-month options, and display these timeframes instead of hard dates UNTIL an apprentice is accepted (when the Maker chooses the actual dates).

[ddgriffin]

Off the top of my head, here are some notes about how we might do this:

Adding the fields

• create a migration to add date fields for start_date and end_date to Signups (then run rake db:migrate)
• on the AppSignup show page, edit the modal that pops up when you hit "Accept" (currently it just asks if you're sure) and add a form to set the start and end date fields

Updating apprenticeship listing for timeframe instead of date range Once we add start and end dates to the app_signups, we want makers to set a timeframe (e.g. "3 months") instead of dates when they create an apprenticeship

• I think we want to keep the begins_at and ends_at fields on the backend, but display a dropdown where they choose a timeframe. Then based on their selected we calculate the ends_at value automatically. Or something.
• The other option would be to scrap those date fields and add a new field onto Events called 'timeframe' (or something) and then adjust anywhere that we currently do calculations off of ends_at

Calculating things once these fields have been set Currently, a lot of things are calculated off of the begins_at and ends_at dates of the apprenticeship; we'd like to switch them over to being calculated off of these new start and end dates. Places to consider include:

• the _leading, _learning, and admin dashboards
• the app_signup show page for Accepted and Confirmed states
• the apprenticeship show page for the apprentice (display her specific start and end dates)
• the apprenticeship show page for the maker (display each apprentice's dates in the list of apprentices
• the emails sent to maker and apprentice following acceptance and confirmation (+ any reminders we want to add)
• the rake tasks that schedule reminders & check-in emails
• the rake tasks that transition an app_signup to closed (currently happens as part of the 'complete_apprenticeships' task based on the ends_at date of the apprenticeship)