Update the used MediaWiki rule set to 0.10.1

[thiemowmde]

I carefully reviewed the new sniffs that come with this version, and I believe they are fine:

• Backtick operators, short casts, and &$this references don't even exist in our code bases, and should not, so these additions are fine.
• We obviously need to allow PHP 7 syntax later when we finally dropped PHP 5 support. But this will take a while and should be done via separate releases. For the moment I suggest to stick to what the MediaWiki rule set does, and not opt-out of this sniff.

Warning, #16 should be merged first!