feat: add support for ! history and readline command in roundup-admin Ad support to change input mode emacs/vi using new 'readline' roundup-admin command. Also bind keys to command/input strings, List numbered history and allow rerunning a command with !<number> or allow user to edit it using !<number>:p. admin_guide.txt: Added docs. admin.py: add functionality. Reconcile import commands to standard. Replace IOError with FileNotFoundError no that we have removed python 2.7 support. Add support for identifying backend used to supply line editing/history functions. Add support for saving commands sent on stdin to history to allow preloading of history. test_admin.py: Test code. Can't test mode changes as lack of pty when driving command line turns off line editing in readline/pyreadline3. Similarly can't test key bindings/settings. Some refactoring of test conditions that had to change because of additional output reporting backend library.

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