Change tabs to spaces.
Bump coding standard.
Apply code formatting for psr-2.
Switch to ccabs.
Fix phpmd violations.
Utilize contao-community-alliance/coding-standard.
Also check against php 5.6.
Drop several codingStandardsIgnoreStart/Stop.
Silence warnings related to $GLOBALS usage where we really need them and some others.
Use translator.
Drop usage of is_null.
Mute some more $GLOBALS usages.
phpDoc.
Exclude some files from phpcpd.
Optimize imports.
Fix translation key for month group header.
Merge branch 'develop' into convert-to-psr-2