This patch introduces new lib/pluginlib.php library that provides
unified access meta-information about all present plugin types. The
library defines plugin_manager singleton that in turn gathers
information about all present plugins and their status. The list of
plugins can be rendered either as plugins check table or plugins control
panel.
This makes print_plugins_table() function obsolete and because it is not
expected to be called by any contrib plugin, the function is removed.
CSS for the legacy table generated by print_plugins_table() is cleaned
up.
