REDCORE-223 add Travis PHP Code Style checker

#do not merge

This is work in progress
Note that I'm adding an exit(0) instead of exit(1). 

The right one should be exit(1) so travis fails if there are code style issues. But right now there are several code style issues to solve in the existing code so Travis would always fail. To prevent it, this script will not make travis fail for the moment but when all code style issues will be fixed we should turn the exit to 1.