labs/incubator phplint job

Change-Id: I7fa86a2c94c7d92b2d0dc91e802f0728105d0395
phplint jobs for mw/skins/*

Creates a PHP linting job for the projects:
- mediawiki/skins/erudite
- mediawiki/skins/mediawiki-strapping
- mediawiki/skins/webplatform

Change-Id: Ideb4dadee06efcec67a7f628936af3724ed256a4