Refactoring migrations by adding an abstract class to all expressions that allow for processing prior to returning an sql statement.

Refactoring the current sql syntax providers to better work with sql ce, sql server and mysql.
Adding migrations for v4.8 and v6.0.
Adding test cases for upgrading from 4.7 to 6.0 for the 3 database providers - sql ce, sql server and mysql.
Adding product name to the MigrationAttribute, which adds more flexibility to the MigrationRunner.
Fixing schema creation for mysql, which broke during a previous refactor task.

src/Umbraco.Core/Persistence/SqlSyntax/SqlSyntaxProviderBase.cs

@@ -161,6 +161,11 @@ namespace Umbraco.Core.Persistence.SqlSyntax
             return true;
         }
 
+        public virtual bool SupportsIdentityInsert()
+        {
+            return true;
+        }
+
         public virtual string Format(TableDefinition table)
         {
             var statement = string.Format(CreateTable, GetQuotedTableName(table.Name), Format(table.Columns));