Rewrite activity log backend to use a query class.

Jellyfin.Data/Queries/ActivityLogQuery.cs

@@ -0,0 +1,30 @@
+using System;
+
+namespace Jellyfin.Data.Queries
+{
+    /// <summary>
+    /// A class representing a query to the activity logs.
+    /// </summary>
+    public class ActivityLogQuery
+    {
+        /// <summary>
+        /// Gets or sets the index to start at.
+        /// </summary>
+        public int? StartIndex { get; set; }
+
+        /// <summary>
+        /// Gets or sets the maximum number of items to include.
+        /// </summary>
+        public int? Limit { get; set; }
+
+        /// <summary>
+        /// Gets or sets a value indicating whether to take entries with a user id.
+        /// </summary>
+        public bool? HasUserId { get; set; }
+
+        /// <summary>
+        /// Gets or sets the minimum date to query for.
+        /// </summary>
+        public DateTime? MinDate { get; set; }
+    }
+}