Add Escapes for Ctrl-Tab Shift-Ctrl-Tab
Ctrl-Tab Shift-Ctrl-Tab are common shortcuts to switch between tabs or panes in applications. Yet VTE ignores Ctrl or Shift-Ctrl modifiers and maps the key combinations to plain tab characters. It will be nice to fix this and use an escape sequences for these characters.
Although there is no standard for encoding these keys, Mintty  uses
^[[1;6I for Ctrl-Tab and Shift-Ctrl-Tab.