---MDL-38147 moved to deprecatedlib.php : make_categories_list()
----- deprecated make_categories_list()
MDL-38147 deprecated category_delete_move(), category_delete_full(), change usage to coursecat
----MDL-38147 moved to deprecatedlib.php : category_delete_move(), category_delete_full()
MDL-38147 deprecated move_category(), course_category_hide(), course_category_show(), change usage to coursecat

All usages in core replaced with:
- coursecat::change_parent()
- coursecat::hide()
- coursecat::show()
-----MDL-38147 moved to deprecatedlib.php : move_category(), course_category_hide(), course_category_show()
MDL-38147 deprecated get_course_category(), change usage to coursecat
------MDL-38147 moved to deprecatedlib.php : get_course_category()
----- deprecated get_course_category()
MDL-38147 deprecated create_course_category(), change usage to coursecat. Also avoid direct DB update of table course_categories

changed to usage of
- coursecat::create()
- coursecat::update()
-------MDL-38147 moved to deprecatedlib.php : create_course_category()
MDL-38147 moved to deprecatedlib.php : get_all_subcategories()
MDL-38147 deprecated get_child_categories(), change usage to coursecat
--------MDL-38147 moved to deprecatedlib.php : get_child_categories()
------ deprecated get_child_categories()
MDL-38147 deprecated get_categories(), change usage to coursecat
-------MDL-38147 moved to deprecatedlib.php : get_categories()
------ deprecated get_categories()
------- deprecated get_categories()
MDL-38147 Performance improvements to coursecat class:

- Retrieve and cache only often-used fields of course category
- Removed function coursecat::get_all_visible() as potentially causing performance issues
- removed function coursecat::get_all_parents() as ineffective and unnecessary, replaced with get_parents()
- retrieve all fields from course_categories when unretrieved field is accessed

Also some code improvements:
- rename functions starting with _ , rename arguments, etc.