missing plugin.info.txt

when downloaded from extension manager under recent dokuwiki, the database2 extension is
detected as database2master, not database2.

This is beause newer DokuWiki use the ``base`` field in new file plugin.info.txt to know the plugin name.

With this patch, extension manager recognises the plugin name and can install database2 properly.

__NB__
method getinfo in class syntax_plugin_database2 uses this file too. Since DW function ``confToHash`` existed before first database2 plugin was released, the change should be compatible with older Doku too.