New features

[4a1d48b] Add flatpickr as a datepicker (@atierant) [4dc4256] Update design to use Bootstrap 4 (@atierant) [4768343] Update the design of the language selector (@javiereguiluz) [0b3e330] Update the design of the source code modal (@javiereguiluz) [ee044c7] Use readonly properties (@COil) [04c1798] Use security roles constants (@COil) [83f8308] Use final classes (@COil)

Maintenance

[dc7ae36] Update recipes (@fabpot) [e1468d2] Update the project to Symfony 6.3 (@javiereguiluz)

Bug fixes

[39fb43c] Fix comment typo (@slodplaadmin)