Add channel desc and channel indicator item. Its meaning and development
examples has been added to overview page in javadoc.
Also removes gt_no_hatch and show_error special button from GUI as they
are now a candidate in the dropdown menu.
one day we will move this to MUI2, but for now let's stick to existing
infra that is known to work
https://github.com/user-attachments/assets/814edbb6-c4b4-4309-8798-787d9ed1aeef
Note: channels in demo video are from GT5. if you boot the pack without
the modified gt5 you won't see most of the channels.
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Signed-off-by: Glease <4586901+Glease@users.noreply.github.com>
