Add parameters to make phpcs more flexible

[jonathan1055]

Currently in lib/stages/coding_style.sh the parameters --standard and --extensions are hard-coded. This is fine as a default, but if a project has its own phpcs.xml(.dist) file then these parameters override it and the customised config file is ignored.

The ideal solution would be to test for the existence of a phpcs.xml file and only if it is not present then add those two parameters to the call.

[jonathan1055]

I'm not sure if this project is still actively managed, so I won't start making a clone and trying out the fix, and making a PR until we have had some discusison. Thanks