If a there exists at some point in the history a class that no longer
exists, Versioned will create it as a `DataObject` as opposed to some form
of the `SiteTree` superclass. This would break the absolute link
funcitonality, so we should make the version at least an instance of
SiteTree so we can generate the link accurately (without fatal errors).
FIX: PSR-2 codebase. Formatting via phpcbf
FIX: rendering bug in allchanges
FIX: update .gitattributes to not export codecov's config file
FIX: Update SiteTree_versions to the ss4 equivalent SiteTree_Versions
Steve Boyd
Dylan Wagstaff
Robbie Averill