Fixed #160 through explicit addition of KEY_TAB

[jgrenda]

Added KEY_TAB to register for accepting the selected method from the autocompletion drow-down window in the node_to_node_configurator dialog.
It is necessary to either undo or prevent the additional focus switch that tab triggered.
As we can't use the find_prev_valid_focus method to do this in the _gui_input method (because we are at the first index) we instead check the key type again in the selected method and prevent additional focus movement if the key type was tab.

[tom95]

Perfect, thank you!