Fixed thumbnails for augmented commerce items

If augmented commerce items (category, product) didn't have a picture url in the commerce system, the thumbnail icon couldn't displayed in CoreMedia Studio even if a picture asset has been assigned (a broken URL was rendered). This has been fixed.

(CMS-25737)

External Page validators enabled

Added two new validator beans for External Pages. External Pages must also be part of the navigation in order to function, hence the new validators check that they are not part of a cycle (recursion) and that they do not have multiple parent nodes. This has so far only been checked for Channels, Augmented Categories and Categories.

(CMS-25651)

Fixed memory issue for blob loading

Fixed possible heap size exceptions when downloading blobs via the Studio REST service.

(CMS-25334)

Handled StackOverflowError While Resolving Default Picture (2nd Fix)

We fixed a bug where a StackOverflowError was thrown while resolving default pictures for cyclicly linked content items. This is the second fix for this problem as the first one was not sufficient.

(CMS-24935)