Fix typo in group mappings help

[#74344702] https://www.pivotaltracker.com/story/show/74344702
Validate group_id and external group in group unmap command

[#74344702] https://www.pivotaltracker.com/story/show/74344702
Require that the group id and external group are provided

[#74344702] https://www.pivotaltracker.com/story/show/74344702
Use group name instead of id for unmap command

[#74344702] https://www.pivotaltracker.com/story/show/74344702
Require external group on map command

[#74344702] https://www.pivotaltracker.com/story/show/74344702
Don't group group mappings by display name

[#74344702] https://www.pivotaltracker.com/story/show/74344702