Ground work for Wino Calendar. (#475)

Wino Calendar abstractions.

Wino.Core.Domain/Entities/Calendar/RecurrenceRule.cs

@@ -0,0 +1,20 @@
+using System;
+using SQLite;
+using Wino.Core.Domain.Enums;
+
+namespace Wino.Core.Domain.Entities.Calendar
+{
+    public class RecurrenceRule
+    {
+        [PrimaryKey]
+        public Guid Id { get; set; }
+
+        public Guid CalendarItemId { get; set; }
+        public CalendarItemRecurrenceFrequency Frequency { get; set; }
+        public int Interval { get; set; }
+        public string DaysOfWeek { get; set; }
+        public DateTimeOffset StartDate { get; set; }
+        public DateTimeOffset EndDate { get; set; }
+        public int Occurrences { get; set; }
+    }
+}