fritzbox binding: adding parameter for username

set fritzbox:user in your openhab.cfg to use telnet login with username and password. Fritzbox must be configured to receive username and password as login.

If no username is provided, ther login procedure falls back to password-only.

(tested with fritzbox 7490, FRITZ!OS 06.21-29577-BETA)
GPIO IO: wait half a second after exporting pin

on raspberry pi, operations on pins fail if executed immediatly after pin export. This change fixes that issue
Merge pull request #1867 from TobiasMende/master

fritzbox binding: adding parameter for username / added sleep() after export in GPIO Binding