NEW: Page types no longer require a controller, they can inherit the parent page type's

Use ClassInfo::ancestry() instead of get_parent_class()

Fall back to ContentController by default
Merge pull request #881 from kinglozzer/framework-1905-controller-inheritance

NEW: Page types no longer require their own controller (fixes silverstripe/silverstripe-framework#1905)
Fix comment typo
Merge pull request #887 from trev/patch-1

Fix comment typo