Fix auto scroll to first event

Issue #50
PR #51

Ability to scroll to a specific time, fix events starting or ending on a different date

1. Ability to scroll to a specific time.

• E.g. Loading the calendar from 8am

2. Fix events starting or ending on a different date

• Previously only the hour and minute of a date are used for calculation.

Relevant pull request by @v-ken #47

Decouple Events and EventViews

1. Created an EventDescriptor protocol describing model for EventView
2. Created an Event class conforming to EventDescriptor protocol
   This class contains algorithm by which all the colors in EventView are calculated.
   If other algorithm is needed to calculate colors, a new class conforming to EventDescriptor protocol could be created
3. Implemented View Reuse

Separating Model (EventDescriptor) from EventView will give two advantages:

1. Possibility to improve internal parts of the library without changing the interface.
2. (In the future) - possibility to register own custom classes for EventView, greatly improving customization.

and some smaller benefit:
Removing DynamicColor dependency completely in the future.

If you're using this library, I'd like to hear your feedback. In most cases, very small changes needed - renaming:

1. Change datasource protocol to func eventsForDate(_ date: Date) -> [EventDescriptor]
2. Setting formatted text as a text property instead of data: [String],
   or subclassing an Event and providing an algorithm, how to calculate text from data,
   or implementing own EventDescriptor.

Scroll to first visible event, bugfixes

PR #45

1. Scroll to first visible event #39
2. Hours are being removed from the left part of the view even if it's not today #44

Expose day view scroll offset, expose ability to set timeline pan gesture's `require(toFail:)` method

1. Expose day view scroll offset:

• Thought it might be useful to get the current scroll offset of the day view. In my case, I use it to determine if it's at the top and if it is, allow other gestures to work, i.e. expanding week/month header view.

2. Ability to set timeline's pan gesture's require(toFail:) method

• Thought it might be useful to allow only certain gestures to work together. I.e. if another pan gesture has been detected, do not allow timeline to scroll. In my case, I use it expand/shrink the week/month header view and not scroll the day view at the same time.
  By @v-ken

NSCopying for CalendarStyle, open access modifiers for delegates

1. Fix issue #35
2. Fix issue #28 using open access modifiers for all delegate implementations in DayViewController

Improvements by @v-ken

Thanks @v-ken !

Changes:

1. BYO header view

• Allow hiding the built-in header view so that users can use their own header views

2. Ability to set current date

• Expose function to set the current date in DayView

3. Maintain date order after a jump

• When jumping dates (by tapping on date in header view instead of swiping), the next swipe back jumps back to the previous date before the jump, instead of the previous date in the calendar. This fixes that issue.

4. Long press in timeline view delegate callback

• Add delegate callback when the timeline view is long pressed in an area without any events

Relevant PR #33

New delegate methods & more customization for EventView

Exposed "date did change" delegate method via day view delegate
UserInfo object in EventView - possibility to store any custom model object to keep track of EventViews
By @danlozano

Added support for non-fullscreen DayView

Added support for non-fullscreen DayView by @diegorozen
Issue: #25
Pull Request #26

Public DataSource/Delegate for DayView

Public DataSource/Delegate for DayView