Add View Results block

[gikaragia]

Overview

As we have removed the 'View Results' buttons in the latest version of the 'My Courses' page and from course progress bar, there isn't a way for users to add a navigation link to the course results page. This PR tries to deal with this issue.

Changes proposed in this Pull Request

• Adds a 'View Results' button block in Sensei courses which navigates to the course results page.

Alternatives considered

• We could possibly look into saving all information in post content to avoid making this a dynamic block. This however would require from users to enclose the block in 'Conditional Content' block, if they want it to be displayed to enrolled users only. Since we didn't follow this approach in other course blocks, I rejected it.
• I also considered adding the block to the course template, but I think that the template feels a bit cluttered already so I avoid it.

Testing instructions

• Add the 'View Results' block in a course.
• With an enrolled user try the block in the frontend.
• Observe that the description of the block is suitable.

[gikaragia]

Add 'View Results' button to the course page

[jom]

Works well! Yeah, for the template it might take some design work. I wonder if we should figure out how to turn them into a button group? Similar to lesson actions, I suppose.

[gikaragia]

I wonder if we should figure out how to turn them into a button group? Similar to lesson actions, I suppose.

Explored this one a bit. I am not sure if supplying them as a group should be the only option as I find it a bit limiting. The ideal way would be for users to be able to add them as a special kind of button in the buttons block. Raised #4160 to track this.