Use cweagans/composer-configurable-plugin

[cweagans]

This converts all configurable values (except the patches array) to use cweagans/composer-configurable plugin.

composer.json configuration now must live in a composer-patches key in extra:

{
    "extra": {
        "composer-patches": {
            "configuration-key": "value"
        }
    }
}

Possible config flags:

exit-on-patch-failure
disable-patching
disable-patching-from-dependencies
disable-patch-reports
patch-levels
patches-file

All of those flags may now be controlled via environment variables:

COMPOSER_PATCHES_EXIT_ON_PATCH_FAILURE
COMPOSER_PATCHES_DISABLE_PATCHING
COMPOSER_PATCHES_DISABLE_PATCHING_FROM_DEPENDENCIES
COMPOSER_PATCHES_DISABLE_PATCH_REPORTS
COMPOSER_PATCHES_PATCH_LEVELS
COMPOSER_PATCHES_PATCHES_FILE

Documentation for these things is forthcoming.

New features in this pull request:

• Ability to disable patch reports
• Ability to specify the patch levels that the plugin will attempt to use when applying a patch
• Ability to disable gathering patches from dependencies

Changes to behavior:

• Some environment variables have been renamed
• Some composer.json flags have been changed
• exit-on-patch-failure is now enabled by default