Added some method inside JDatabaseDriver to create database and alter character set [v2]

Added two public method inside JDatabaseDriver:
- alterDbCharacterSet to change database's character set
- createDatabase to create a new database

AlterDbCharacterSet needs database name as parameter, createDatabase needs a JObject, similar to that used inside CMS' "initialise" function, and a bool to set UTF8 database's support.

They use two protected method to obtain correct query in database's
supported syntax:
- getAlterDbCharacterSet
- getCreateDatabaseQuery

Protected method inside JDatabaseDriver return query for MySQL and MySQLi syntax, this commit contain also overridden version for PostgreSQL database.

There are tests only for protected methods inside MySQL, MySQLi and PostgreSQL test classes.

[Old Pull request](https://github.com/joomla/joomla-platform/pull/1261)