fix(config): remove default key bindings for input broadcasting (#40)

Accidental activation of this feature may be dangerous.
This change forces users to assign a binding manually.

See https://bugs.launchpad.net/terminator/+bug/1872460

terminatorlib/config.py

@@ -180,9 +180,9 @@ DEFAULTS = {
             'ungroup_tab'      : '<Shift><Super>t',
             'new_window'       : '<Shift><Control>i',
             'new_terminator'   : '<Super>i',
-            'broadcast_off'    : '<Alt>o',
-            'broadcast_group'  : '<Alt>g',
-            'broadcast_all'    : '<Alt>a',
+            'broadcast_off'    : '',
+            'broadcast_group'  : '',
+            'broadcast_all'    : '',
             'insert_number'    : '<Super>1',
             'insert_padded'    : '<Super>0',
             'edit_window_title': '<Control><Alt>w',