Move presenters to own namespace.

To try and discourage their use outside control templates.

Perspex.Controls/Perspex.Controls.csproj

@@ -40,7 +40,7 @@
     <Compile Include="ColumnDefinition.cs" />
     <Compile Include="ColumnDefinitions.cs" />
     <Compile Include="ContentControl.cs" />
-    <Compile Include="ContentPresenter.cs" />
+    <Compile Include="Presenters\ContentPresenter.cs" />
     <Compile Include="Control.cs" />
     <Compile Include="ControlExtensions.cs" />
     <Compile Include="Controls.cs" />
@@ -63,7 +63,7 @@
     <Compile Include="Generators\IItemContainerGenerator.cs" />
     <Compile Include="ItemsControl.cs" />
     <Compile Include="ItemsPanelTemplate.cs" />
-    <Compile Include="ItemsPresenter.cs" />
+    <Compile Include="Presenters\ItemsPresenter.cs" />
     <Compile Include="Panel.cs" />
     <Compile Include="RowDefinition.cs" />
     <Compile Include="RowDefinitions.cs" />

Perspex.Controls/ContentPresenter.cs → Perspex.Controls/Presenters/ContentPresenter.cs

@@ -4,7 +4,7 @@
 // </copyright>
 // -----------------------------------------------------------------------
 
-namespace Perspex.Controls
+namespace Perspex.Controls.Presenters
 {
     using System;
     using System.Linq;

Perspex.Controls/ItemsPresenter.cs → Perspex.Controls/Presenters/ItemsPresenter.cs

@@ -4,7 +4,7 @@
 // </copyright>
 // -----------------------------------------------------------------------
 
-namespace Perspex.Controls
+namespace Perspex.Controls.Presenters
 {
     using System;
     using System.Collections;

Perspex.Controls/TabStrip.cs

@@ -10,6 +10,7 @@ namespace Perspex.Controls
     using System.Collections;
     using System.Linq;
     using Perspex.Controls.Generators;
+    using Perspex.Controls.Presenters;
     using Perspex.Input;
 
     public class TabStrip : SelectingItemsControl

Perspex.Controls/TreeView.cs

@@ -11,6 +11,7 @@ namespace Perspex.Controls
     using System.Linq;
     using System.Reactive.Linq;
     using Perspex.Controls.Generators;
+    using Perspex.Controls.Presenters;
     using Perspex.Input;
 
     public class TreeView : SelectingItemsControl