Add parsing of PL extra section in main project's composer.json

[aleksip]

It seems that a possible Pattern Lab extra section in the main project's composer.json is not parsed apart from starterKitSuggestions when running composer create-project.

This would be a nice feature to have for setting config options in an edition's composer.json.

[dmolsen]

Config options can now be set in an edition's composer.json. This feature is supported in the feature-installupdate branch of the development edition and core. A couple of notes...

• the config options from an edition's composer.json are applied after everything else has been installed. this way any option set by a package can be overridden on a per edition basis.
• the override is done silently
• i need to look at overriding options with arrays. this is a general issue with the composer.json config set-up. going to use a spin-off of sayings to test this.

[dmolsen]

Arrays should be handled. With no other other comments on the process I'm going to take this feature as done and will be implementing with the push of the feature-installupdate branch towards a release.