php-cs-fixer workflow

[connorhu]

As we talked about it, we could make a github action to test php coding standards (later maybe code sniffer).

This is a tested config for push event:
FriendsOfSymfony1/doctrine1@master...connorhu:doctrine1:feature/phpcsfixer
master...connorhu:symfony1:feature/phpcsfixer

I have to test it for PR event, but it works for push. When I have tested for PR I will make a pull request. The cs-fixer setting is left at minimum (only tests what @thePanz noticed to in my PR at FriendsOfSymfony1/doctrine1#94 ).
It's another question of what the setting should be at all. @symfony ruleset would be logical, but it's a very aggressive and generates a very different style from current code formatting.

We should only test the files we touch.

[thePanz]

Fixed in #283