Add feature to check if package name is already taken on Packagist

[raphaelstolt]

[jonathantorres]

We could name the command construct packagist:check.

Packagist API: https://packagist.org/apidoc

Maybe use the "Get package by name" endpoint. Use guzzle or curl to make the requests.

[raphaelstolt]

Would that really be a own command, and not an optional option which halts the further construction and produces a warning to choose an alternative package name?

[jonathantorres]

Sure, It can be done as an optional option. It should display a warning, but not stop the construction of the project.