New variables for the DP750 to allow the following settings:
$grandstream_repeater_mode_enable
(Enables or disables repeater mode on DP750 base)
$grandstream_hanging_group_mode
(Allows users to set hanging group mode (e.g. ring handsets at the same time, sequentially, etc.)
$grandstream_handset_X_line_Y_enable
(Allows setting of handset to line assignment)