Plugins may use this general tool for uninstallation and eventually
removal of the deployed source code. At the moment, this is implemented
as a wrapper for the core function uninstall_plugin() with an extra hook
in the relevant plugin info subclass.
For non-standard add-ons, the tool can remove the deployed plugin source
code as well, if the web server has required write permissions. Ideally,
all add-ons installed via the new tool_installaddon should be removable
via the web interface as well.
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.
