Refactoring usage of DatabaseType - more convention based.

Limiting the use of the DatabaseType, so its only used for NText and NChar.
Adding LengthAttribute for fixed sized columns.

src/Umbraco.Core/Persistence/DatabaseAnnotations/DatabaseTypeAttribute.cs

@@ -1,16 +0,0 @@
-using System;
-
-namespace Umbraco.Core.Persistence.DatabaseAnnotations
-{
-    [AttributeUsage(AttributeTargets.Property)]
-    public class DatabaseTypeAttribute : Attribute
-    {
-        public DatabaseTypeAttribute(SpecialDbTypes databaseType)
-        {
-            DatabaseType = databaseType;
-        }
-
-        public SpecialDbTypes DatabaseType { get; set; }
-        public int Length { get; set; }
-    }
-}

src/Umbraco.Core/Persistence/DatabaseAnnotations/LengthAttribute.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace Umbraco.Core.Persistence.DatabaseAnnotations
+{
+    [AttributeUsage(AttributeTargets.Property)]
+    public class LengthAttribute : Attribute
+    {
+        public LengthAttribute(int length)
+        {
+            Length = length;
+        }
+
+        public int Length { get; private set; }
+    }
+}

src/Umbraco.Core/Persistence/DatabaseAnnotations/SpecialDbTypeAttribute.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace Umbraco.Core.Persistence.DatabaseAnnotations
+{
+    [AttributeUsage(AttributeTargets.Property)]
+    public class SpecialDbTypeAttribute : Attribute
+    {
+        public SpecialDbTypeAttribute(SpecialDbTypes databaseType)
+        {
+            DatabaseType = databaseType;
+        }
+
+        public SpecialDbTypes DatabaseType { get; private set; }
+    }
+}