New Command Line Groupings

[dadgar]

This PR:

• Moves all our commands into the grouped subcommand pattern
• Calls out common commands
• Adds colored output
• Redirects help to stdout
• Displays deprecated commands
• Displays aliased commands in help output
• Adds more descriptive help output to parent commands (e.g. nomad node)
• Updates the documentation to the new command format and fixes a lot of inconsistencies

[preetapan]

Should this old alias client config be mentioned in the docs ?

[dadgar]

I only called out aliases we want to keep. Like shortcuts. We will need to add a version section to: https://www.nomadproject.io/docs/upgrade/upgrade-specific.html

[preetapan]

LGTM - Its hard to tell if you missed any string search replace spots in the documentation where the old style commands were used, but we can handle that as we see them,

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