Command queue

New: Adding multiple series will queue them instead of running all at once
New: Slower scheduled tasks won't be block others from running

src/NzbDrone.Core/Datastore/Converters/TimeSpanConverter.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Globalization;
+using Marr.Data.Converters;
+using Marr.Data.Mapping;
+using NzbDrone.Common.Extensions;
+
+namespace NzbDrone.Core.Datastore.Converters
+{
+    public class TimeSpanConverter : IConverter
+    {
+        public object FromDB(ConverterContext context)
+        {
+            if (context.DbValue == DBNull.Value)
+            {
+                return TimeSpan.Zero;
+            }
+
+            return TimeSpan.Parse(context.DbValue.ToString());
+        }
+
+        public object FromDB(ColumnMap map, object dbValue)
+        {
+            if (dbValue == DBNull.Value)
+            {
+                return DBNull.Value;
+            }
+
+            if (dbValue is TimeSpan)
+            {
+                return dbValue;
+            }
+
+            return TimeSpan.Parse(dbValue.ToString(), CultureInfo.InvariantCulture);
+        }
+
+        public object ToDB(object clrValue)
+        {
+            if (clrValue.ToString().IsNullOrWhiteSpace())
+            {
+                return null;
+            }
+
+            return ((TimeSpan)clrValue).ToString("c", CultureInfo.InvariantCulture);
+        }
+
+        public Type DbType { get; private set; }
+    }
+}