Username validation function

src/freedombone-app-blog

src/freedombone-app-emacs

src/freedombone-app-irc

src/freedombone-app-syncthing

src/freedombone-app-tahoelafs

src/freedombone-app-xmpp

src/freedombone-archive-mail

src/freedombone-backup-local

src/freedombone-backup-remote

src/freedombone-base-email

src/freedombone-controlpanel

src/freedombone-restore-local

src/freedombone-restore-remote

src/freedombone-sec

src/freedombone-syncthing

src/freedombone-utils-backup

src/freedombone-utils-validation