Move groups component check to setup_actions() to always return the singleton instance
Move admin bar New Group node code for BP Group Organizer to its own class
Update @since phpDoc headers for BPGUM_Organizer methods
New p_group_user_management_loaded hook after setup_actions
Reorder loading hooks in BPGUM_Organizer

* Setup `extend` property of the main plugin class to which extending classes should attach
* Load class at `bp_group_user_management_loaded` hook
* Load class in `bp_group_user_management->extend`
* Load organizer admin page hooks in separate `admin_page()` method which is loaded during the admin page load
Remove BPGUM_Hierarchy extension class and dedicated file. Has never been used.
Stricter ABSPATH page access check
Undo using BuddyPress's textdomain
Update Dutch translation
Move is-plugin-active check for BP Group Organizer to the plugin extend file