Gui dialogs (#410)

* started refactoring for gui windows

* a bit more work on gui windows

* fixed some bugs and broken build stuff

* fixed some bugs in gui controls

* a little code cleanup

* got gui dialogs positioning and experimenting with named styles by type

* apply control styles directly in the constructor of controls

* got everything compiling again

* all gui controls have skinnable constructors

* rework uniform grid desired size calculations

* turns out gui layouts are complicated

* include pdb files in nuget packages

* fixed a bug in find nearest glyph

* custom control styling

* added a range constructor overload that takes one value

* rethinking control desired size behaviour

* made particle emitters more editable at runtime

* moved the auto trigger code to the particle effect instead of the emitters

* tweaks

* changed the particle modifer interface to an abstract base with an optional name

* changed the particle modifer interface to an abstract base with an optional name

* an attempt at creating a gui combo box

* rolled back the nested control experiment

* pretty good (but not perfect) combo boxes

* tweaks

* name property bindings on lists

* removed and cleaned up the hacks from the gui combo box

* minor combo box styling tweaks

* minor bug fix in gui combo box

* experiments with data binding

* fixed a mistake on the texture region service interface

* working on the ability to serialize particles

* finished particle serialization

* more robust range deserialization

* added editor browable attributes

* fixed some broken demos

* made the particle modifiers editable at runtime

* fixed some issues with particle serialization

* fixed some issues with interpolators

Source/MonoGame.Extended.Particles/Modifiers/DragModifier.cs

@@ -2,12 +2,12 @@
 
 namespace MonoGame.Extended.Particles.Modifiers
 {
-    public class DragModifier : IModifier
+    public class DragModifier : Modifier
     {
         public float DragCoefficient { get; set; } = 0.47f;
         public float Density { get; set; } = .5f;
 
-        public unsafe void Update(float elapsedSeconds, ParticleBuffer.ParticleIterator iterator)
+        public override unsafe void Update(float elapsedSeconds, ParticleBuffer.ParticleIterator iterator)
         {
             while (iterator.HasNext)
             {