generic PHP plugin config system

With just a little comment block following the new PHP plugin standard, ordinary PHP scripts are turned into manageable modules. This admin interface in particular allows to enable and disable plugins online or to set any of the easily defined options. It saves plugin loading commands and variable/constant assignments into a simple config.php (which never gets overwritten, but non-destructively edited). Using this config.php script to load associated web project / cms / portal script modules is of course much faster and more straightforward than INI files or holding configuration data in a SQL table.