Update README.md

Fixing connection issues to MySQL 8.0.4

Fixing connection issues to MySQL 8.0.4.

Fix get involved link

Providers should not be able to create appointments for other providers in the backend calendar page. #510

Updated GDPR related french translations (oxteam). 

Update of the translation files.

Import system translations from official CI depot https://github.com/bcit-ci/codeigniter3-translations

Only files already existing in EA! were imported.

CI's portuguese-brazilian folder was used for EA!'s portuguese-br.
CI's simplified-chinese folder was used for EA!'s chinese folder.

No supported translations exists for Finish and Luxembourgish. The migration_lang files for these languages are still in English but one translation key is missing compared to the EA! English original file.
For consistency purpose, the Finish and Luxembourgish migration_lang files have been overwritten by the EA! English original file.

All files have their tags now ordered like in the English one, duplicate tags are removed and the Arabic file has the "about_ea*" tags changed to "about_app*" like in other languages.
In additon for the French language, improved some translations (mainly consistency in usage of infinitive verb forms).

Merge branch 'oxteam-patch-fr_trans-1' of https://github.com/oxteam/easyappointments into oxteam-oxteam-patch-fr_trans-1

Corrected typo in german translations.

Performance optimization in backend calendar page, after the user clicks the insert appointment button. (#500)