Revised the settings system

* Settings now reside in a special INI file (site dir)
* Added an advanced INI parser that decodes JSON values
* Renamed settings section "core" to "main"
Improved the System class

* Added getters for settings and database driver
* Made the class failsafe
Added function ww_setting()
Make use of function ww_setting()
Revised the Database class
Converted Database::loadDriver() to function ww_open_db()