The method should check against $CFG->disableupdatenotifications and not
$CFG->disableupdateautodeploy. This had to be a copy&paste mistake from
the \core\update\deployer::enabled().
While looking at it, I also fixed couple of places where this method
should and could be used.
These are cosmetic improvements spotted while working on the issue.
1. Do not waste time if there are no changes to notify about.
2. Fix the legacy plugin manager's get_plugins() call.
Includes:
* update checker refactored to \core\update\ namespace
* plugininfo classes refactored to \core\plugininfo\ namespace
* plugin_manager renamed to core_plugin_manager
* redirect back to original page after plugin uninstall
* fixed assign subplugin uninstall
* move assign subplugins under the assignment in admin tree
* fixed plugininfo for all question related plugin types
* auth uninstall support
* added missing block dependencies
* added theme uninstall
* subplugin types are following the plugin on plugin overview page
* several performance improvements in plugin manager
* new warnigns when plugininfo are outdated or missing
* multiple fixes and other improvements
