Multiple Installs enabled on MicroCMS

Since MicroCMS is not resource consuming for your database, it has two tables so far, you might be tempted to have multiple installs on one database. Before we do this, we should allow prefixes for the tables as for the mainstream CMS. It's done now, MicroCMS supports the variable prefixes when it queries the database. the install process of MicroCMS is not automated, you must be proficient with a little SQL, but nothing hard so far. Also the core class was modified to support variable table prefixes.