Improve CLI --help documentation

[cdrage]

Separates the commands into appropriate categories.

Example:

Usage:
  odo [command]

Examples:
  # Creating and deploying a Node.js project
  git clone https://github.com/openshift/nodejs-ex && cd nodejs-ex
  odo create nodejs
  odo push

  # Accessing your Node.js component
  odo url create

Component Commands:
  component   Components of application.
  create      Create a new component
  delete      Delete an existing component
  describe    Describe the given component
  link        Link target component to source component
  list        List all components in the current application
  log         Retrieve the log for the given component.
  push        Push source code to a component
  update      Update the source code path of a component
  watch       Watch for changes, update component on change

Other Commands:
  app         Perform application operations
  catalog     Catalog related operations
  project     Perform project operations
  storage     Perform storage operations
  url         Expose component to the outside world

Utility Commands:
  completion  Output shell completion code
  help        Help about any command
  version     Print the client version information

Flags:
  -h, --help      help for odo
  -v, --verbose   Verbose output

Use "odo [command] --help" for more information about a command.

[cdrage]

Closes #470

Ping @kadel

[surajnarwade]

@cdrage , component commands, Other Commands etc options should not be printed if there's nothing into it

$ odo url
Expose component to the outside world.
....
....
Component Commands:

Other Commands:

Utility Commands:
...
...

[cdrage]

@surajnarwade @kadel

This should work normal now 👍

Problem was that setting setUsageTemplate to rootCmd changes all the children, when we just want to change it for doing odo --help.

Setting a standard cmdUsageTemplate to each child, fixed it!

[surajnarwade]

@cdrage , LGTM now