Improvements and bug fixes from Moodle Academy

Several minor bug fixes.
Update code to coding standards.
Translations are saved under the foundhash to avoid accidentally overwriting translations.
Introduced CLI scripts to replace duplicate translation hashes and copy translations.
Introduced scheduled tasks to replace duplicate translation hashes, copy translations, insert translation spans, and clean up translation issues table.
Introduced a translations history table.
Moodle 4+ compatibility.
Fixes #164.
Update readme.

andrewhancox / moodle-filter_translations