New features

[d59a50f] Migrated from HTMLPurifier to html-sanitizer (@tgalopin) [380a07e] Added missing return types (@Coderberg) [a50e3e4] Added PHP 7.3 to Travis CI tests (@Coderberg) [0a99a78] Updated dependencies to Symfony 4.2.3 (@javiereguiluz)

Bug fixes

[d911861][9c1f379] Fixed Russian translation (@yceruto) [4e03903] Fixed the handling of flash messages (@Matvien) [5418747] Updated some contents to make them more inclusive (Raphaëll Roussel)