Adds possibility to retreive userlist from Fritzbox at startup

[RoSchmi]

This little supplement to the library gives the possibility to retrieve the userlist from the Fritzbox to enable the selection through a combobox in a GUI or to give a preset of the last user in a console application (implemented in my branch developRoSchmi). May be that this can be done in a better way, but I thought that perhaps you would like it. Many thanks for your valuable code. RoSchmi