MDL-46567 gradereport_history: Initial commit with basic structure of the report
MDL-46567 gradereport_history: Prevent duplicate username column from rendering
MDL-46567 gradereport_history: Fix bug with paging
MDL-46567 gradereport_history: Move paging implementation to db layer
MDL-46567 gradereport_history: Extra version.php info
MDL-46567 gradereport_history: Basic readme.md
MDL-46567 gradereport_history: Basic codestyle, phpdocs and other minor cleanups

This commit includes following changes:-
- Fix codestyle issues
- Remove readme file
- Fix and add file headers
- Fix and add missing phpdocs
MDL-46569 gradereport_history: Move class gradereport_history_user_button to proper namespaced location
MDL-46569 gradereport_history: Move class gradereport_history_filter_form to proper namespaced location
MDL-46569 gradereport_history: Create a helper class
MDL-46569 gradereport_history: Use table_sql for the report

This patch includes:-
- Convertion of the code to use new renderable/renderer apis
- Rewrote the code to remove all custom sorting, etc and use table sql instead
- Usernames are now clickable
- Grade items are now clickable
- Grade history is now displayed even if the grade item is deleted
- We are now using table sql for downloads so export in multiple formats is supported
- Feedback is now properly formatted
- Source fields are not capitilised anymore
- Paging is not shown on top of filters anymore
MDL-46574 gradereport_history: added report viewed event
MDL-46570 gradereport_history: Converting JS to namespace'd module
MDL-46570 gradereport_history: Safer use of language strings
MDL-46570 gradereport_history: Convert to use templates and selectors
MDL-46570 gradereport_history: Simplifying the select/deselect buttons logic
MDL-46570 gradereport_history: Adding JS documentation
MDL-46570 gradereport_history: Convert to moodle dialogue
MDL-46570 gradereport_history: Improving accessibility and selection mechanism
MDL-46570 gradereport_history: Reworked search and load more mechanism