1. Add ctype, iconv and mbstring polyfills to limit required extensions.
2. Add badges to indicates required/optional state.
3. Add description on some requirements.
4. Add openssl to optional required extensions.
5. Reword titles/valdiation messages.
6. Group some checks to improve readability.

* Drop PHP 7.3 support

* Update .github/workflows/ci.yml

Co-authored-by: Guillaume Bougard <gbougard@teclib.com>

Co-authored-by: Guillaume Bougard <gbougard@teclib.com>

The previous badge referenced the CI status for 9.3 branch instead.

- Update moment.js from 2.19.3 to 2.22.2
- Update lodash.js from 4.17.4 to 4.17.11
- Update TinyMCE from 4.7.13 to 4.9.0
- Update prism.js from 1.5.1 to 1.15.0
- Update leaflet.js from 1.2.0 to 1.3.4
- Update leaflet.markercluster.js from 1.2.0 to 1.4.1
- Update FontAwesome from 5.4.1 to 5.5.0
- Update jQuery from 1.10.2 to 1.12.4
- Update jQuery FullCalendar from 3.6.1 to 3.9.0
- Update jQuery File-Upload from 5.34.0 to 9.28.0
- Update jQuery Timepicker Addon from 1.5.0 to 1.6.3
- Update jQuery jstree from 3.3.4 to 3.3.7
- Load not minified file in debug mode if file exists
- Update dependencies versions in README file

* review image/upload in richtext editor
* condition tinymce paste_data_images param with presence of fileupload placeholder
* condition tinymce paste plugin on presence of tinymce
* delay tinymce loading
* Do not follow links using "onclick" (on dialog open only)

Add a constant for minimal PHP version
drop password_compat anid array_column that are native in PHP 5.5