Fix repetition in masked/cropped node name

Summary: By default, bounding boxes are named "<image name> Bounding Shape". Since the name of nodes created by masking/cropping is "<image name>_<bounding box name>_masked/cropped", this often leads to repetition. Although one could argue this is by design, I propose to check if the new nodes' name already starts with the name of the original image before prepending it again. Fixes T29092

Test Plan: Use the Image Cropper plugin to create a new bounding box and mask or crop an image. Change the name of the bounding box and repeat. The newly created node should always start with the name of the original image, but not repeated twice.

Reviewers: O3 MITK Reviewer Group II, floca

Reviewed By: O3 MITK Reviewer Group II, floca

Maniphest Tasks: T29092

Differential Revision: https://phabricator.mitk.org/D616