Add debug mode for dependency graph

[pulse00]

Background

When being in dependency hell, especially for deeply-nested transitive dependencies, composer error messages can get really confusing.

Idea

Provide the composer dependency graph with a Debug mode that does the following

• Load the local composer.json file
• Build a tree for the local dependencies via packagist.org
• Visualize the dependencies including versionnumbers

This way the graph can be used to visualize the actual problem and hopefully make dependency hell a thing of the past ;)

[pulse00]

See composer/composer#1827

[KeKs0r]

+1

[spidgorny]

+1