Particles data driven (#388)

* yay, a start on data driven particles

* added data driven support for all particle profiles

* pretty much finished all of the particle serialization code

* resolved an inconsistency with the interpolators

Source/MonoGame.Extended.Particles/Serialization/ModifierExecutionStrategyJsonConverter.cs

@@ -0,0 +1,24 @@
+using System;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+
+namespace MonoGame.Extended.Particles.Serialization
+{
+    public class ModifierExecutionStrategyJsonConverter : JsonConverter
+    {
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        {
+        }
+
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            var value = JToken.Load(reader).ToObject<string>();
+            return ParticleModifierExecutionStrategy.Parse(value);
+        }
+
+        public override bool CanConvert(Type objectType)
+        {
+            return objectType == typeof(ParticleModifierExecutionStrategy);
+        }
+    }
+}