Show info header only on first command

[ahangarha]

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Closes #111

[ahangarha]

In b38664f, I used class variable because I couldn't implement the solution using a class instance variable.

In 16a829f, I used class instance variable but with a cost of exposing show_info_header as public interface and calling it with Cpl::Cli.show_info_header

[rafaelgomesxyz]

Looks good to me, just one thing I missed about initializing the variable, but no need for re-review.

[justin808]

LGTM

[justin808]

@ahangarha clear on why this is better?

[ahangarha]

clear on why this is better?

Sure!