MDL-42078 multiple uninstall improvements and cleanup

Includes:
* 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
* forbid "base" and "general" as plugin names in core_component (previously blacklisted in plugin manager)
* multiple fixes and other improvements