Merge: src/doc/commands: clean commands hierarchy

This PR does some cleaning around commands hierarchy to prepare for the merge with new-markdown (#2720).

Pull-Request: #2723

diff --cc src/doc/commands/commands_base.nit
Simple merge

diff --cc src/doc/commands/commands_catalog.nit
Simple merge

diff --cc src/doc/commands/commands_http.nit
Simple merge

diff --cc src/doc/commands/commands_parser.nit
Simple merge

diff --cc src/doc/templates/tests/test_json_commands.nit
Simple merge

diff --cc src/doc/templates/tests/test_json_commands.sav/test_cmd_mentities.res
Simple merge

diff --cc src/doc/term/term.nit
Simple merge