Add task for composer-require-checker

[jyggen]

Q	A
Branch	master
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Documented?	yes
Fixed tickets	-

Adds support for composer-require-checker.

A CLI tool to analyze composer dependencies and verify that no unknown symbols are used in the sources of a package. This will prevent you from using "soft" dependencies that are not defined within your composer.json require section.

New Task Checklist:

• Is the README.md file updated?
• Are the dependencies added to the composer.json suggestions?
• Is the doc/tasks.md file updated?
• Are the task parameters documented?
• Is the task registered in the tasks.yml file?
• Does the task contains phpspec tests?
• Is the configuration having logical allowed types?
• Does the task run in the correct context?
• Is the run() method readable?
• Is the run() method using the configuration correctly?
• Are all CI services returning green?

[veewee]

@jyggen, Thanks for the PR! Can you resolve the conflicts? The code looks good to me!

[jyggen]

@veewee Done!

[veewee]

Thanks!