Merge upstream develop (rebasing DB changes)

.gitignore

assets/default/about-custom-themes.md

assets/default/css/print.css

assets/default/css/theme.css

assets/default/css/theme.min.css

assets/default/less/base.less

assets/default/less/kb.less

assets/default/less/landing-page.less

assets/default/less/main-layout.less

assets/default/less/print.less

assets/default/less/reset.less

assets/default/less/theme.less

assets/default/less/ticket-forms.less

assets/default/less/ticket.less

include/class.config.php

include/class.file.php

include/class.format.php

include/class.misc.php

include/class.nav.php

include/class.upgrader.php