Add composer.json
Add composer.json

This add php parallel lint test. Can be triggered using the entry
point:

 composer test

That ease Jenkins integration and let developers add more testing
utilities as needed.

Change-Id: I2bf0dbea9f559267001eb727c7ecfeb103717464

wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo,wikimedia/mediawiki-extensions-Echo