Plugins which implement their own listCommands method should pass their
non-typically discoverable commands to Commands.listCommands via this
mechanism. This means that the de-duplication of commands is performed in one
spot instead of having each plugin implement it on their on in their
listCommands method.
This reverts commits 0ce829af6215b97e725f4d6d580d1151950be869 and
09fb0e6fc974445a3414fb03a94625f8538d4570.
Signed-off-by: James Vega <jamessan@users.sourceforge.net>