Fixed persistency layer.

Now we have ODBC .. that accepts various connection string (including SQLite, MySQL,...)
  And EiffelStore+MySQL.
Updated sql scripts to work with MySQL, and SQLite.
Added a sql_statement (s: STRING): STRING that converts ROC sql statement to fit the underlying database engine.
 mostly to adapt incompatibilities such as AUTO_INCREMENT for MySQL and AUTOINCREMENT for SQLite
 by default SQL script should be written following MySQL SQL syntax.
Warning: to use ODBC persistence driver, it has to be installed on the target machine.

library/persistence/implementation/store/database/database_config.e

@@ -8,16 +8,16 @@ deferred class
 
 feature -- Database access
 
-	hostname: STRING = ""
+	default_hostname: STRING = ""
 			-- Database hostname.
 
-	username: STRING = ""
+	default_username: STRING = ""
 			-- Database username.
 
-	password: STRING = ""
+	default_password: STRING = ""
 			-- Database password.
 
-	database_name: STRING = "EiffelDB"
+	default_database_name: STRING = "EiffelDB"
 			-- Database name.
 
 	is_keep_connection: BOOLEAN