Updates to installer for xoop_lib location and Doctrine

Present path definitions early, so we can use code from XOOPS and vendor libraries more freely.
Convert all database access to Doctrine or XOOPS system calls. It still defines $xoopsDB for legacy support when core code being called still depends on it.
Extended database driver selection to include all platforms Doctrine supports. These will be presented for TESTING and EXPERIMENTAL use only. At present, the PDO MySql driver is the only one offically supported. The list presented is sensitive to what is available and installed in PHP. In addition to MySql, there is support for SqLite, PostGreSql, Sql Server, Oracle and IBM DB2. There are still issues in core when using anything but PDO MySql or MySqli drivers, but progress is being made, and an installer that can generate test cases is an important step.
A new format was introduced to pass the varied information required by new drivers from installation to the running system using xoops_data/data/secure.php. XOOPS_DB_PARAMETERS is a serialized array of connection information that can be presented to the connect function. The familiar XOOPS_DB_* defines are still populated, but are not directly used to establish the database connection, unless the XOOPS_DB_PARAMETERS array is not set.