Support zoom in/out for mockups for reviewers

The ability to create mockups within Aha! to illustrate simple flows or concepts it great. However, it can be difficult for reviewers to read some of the information displayed in the mockup in "review" mode because the image gets fitted within the available space.  It would help if reviewers could zoom in and out and move around using the right-click and alt+mouse wheel combinations that are available in the "edit" mode. We would prefer to keep all conversations within Aha! instead of using external tools to achieve the same.