Handling recurring constraints

[gskorokhod]

For the sake of flexibility we need to be able to add recurrence rules to constraints.
For example:

• "This person cannot work Mondays and Tuesdays every week"
• "This person is on a 5/2 schedule, so needs to have 5 consecutive work days and 2 consecutive weekends every week"
• "This location is unavailable on Mondays from 12 to 3 every other week"

etc

Essentially, we will need to implement a subset of RFC5545

[gskorokhod]

A quick search gave me the RSchedule library but it seems to be unmaintained

[gskorokhod]

For now, the best choice seems to be this: https://github.com/jkbrzt/rrule

[gskorokhod]

That, or write our own minimal implementation of it
(we dont need all of ical or really all of rrule I think)

[gskorokhod]

There is also a full implementation of the ical format in javascript: https://github.com/kewisch/ical.js

[gskorokhod]

Will work on this later, need the UI done first

[gskorokhod]

Drafted a design for handling recurring shifts here: #35
An RFC on constraints will be done soon, and then I will work on implementation