Improve checkout command usability.
Improve choosing environments in get command.
Mark the current environment in the checkout options.
List environments if 'platform branch' is called with no arguments.
String consistency
Fix undefined $environmentList
Merge master into fix-branch-wait--fix-checkout, resolves #135

Conflicts:
	src/Command/EnvironmentListCommand.php
	src/Command/ProjectGetCommand.php
Revert "Support Sf2-style option specs."

This reverts commit e905055b63a26ed90802b8f89cab7b68a0a01306.