task #8608 : Add checkbox to show birthdays in calendar view

htdocs/actioncomm.class.php

htdocs/comm/action/fiche.php

htdocs/comm/action/index.php

htdocs/contact/perso.php

htdocs/langs/en_US/agenda.lang

htdocs/langs/en_US/companies.lang

htdocs/langs/en_US/other.lang

htdocs/langs/es_ES/companies.lang

htdocs/langs/es_ES/other.lang

htdocs/langs/fr_BE/companies.lang

htdocs/langs/fr_FR/agenda.lang

htdocs/langs/fr_FR/companies.lang

htdocs/langs/fr_FR/other.lang

htdocs/langs/nl_BE/companies.lang