Image Annotations for Visual Review tool

With https://gitlab.com/gitlab-org/gitlab-ce/issues/53390 we provided the ability for users to manually review the visual and application changes within a review app.

As the next iteration, we want to enable users to easily annotate the screenshots that they take with the Visual Review tool. This should include:

• Color selection
• Freestyle "brush" drawing
• Create a rectangle and/or circle around something to highlight it
• Point an arrow at an element in the screenshot
• Blur a part of the image to obscure it
• Add some text to the image

See this example: Mar-08-2019_14-44-21