Check for autoloader path when installed as global composer dependency

[gapple]

This checks for the autoloader path when launcher is either installed as a phar, or globally with composer via composer global require drupal/console-launcher.

Running console from a global install via composer still fails after this change, but it's due to the paths in DrupalConsoleCore::boot() being unaware of being run via console-launcher globally or from a project via console, and consequently neither console-launcher/services.yml or console/services.yml are loaded as required.

#120