Rename YCalendarPicker and YCalendarView

[Mark Pospesel]

Intro

We should reserve the Y prefix for our framework names not for objects within our classes.

Tasks

1. Rename YCalendarPicker (and file names) to CalendarPicker
2. Rename YCalendarView (and file names) to CalendarView
3. Rename Classes folder to UIKit
4. Rename Views folder to SwiftUI
5. So that this is not a breaking change, let's add a type alias from the old names:

/// UIKit month calendar picker
///
/// Renamed to `CalendarPicker`.
@available(*, deprecated, renamed: "CalendarPicker")
public typealias YCalendarPicker = CalendarPicker

/// Swift UI month calendar picker
///
/// Renamed to `CalendarView`.
@available(*, deprecated, renamed: "CalendarView")
public typealias YCalendarView = CalendarView