Enable Test Case Preview

[no-stack-dub-sack]

In #208 changes were made to opt-in to running challenge tests on initial load. As a result, since the workspace only "knows" what the test messages are after they've been run at least once, there was no way for the user to see the test cases they were meant to satisfy without running the tests.

This PR aims to improve UX by allowing the user to preview the test cases without requiring a test run (for non-markup challenges only). The idea is to use a regex to extract test messages from test code and create a set of "preview" test cases from these messages to set as the initial test result state. This required some minor refactoring to the TestResultRow component to properly show that the tests are in a default/non-run state.

How this looks:

In action:

Other small changes:

• Add tooltip to error icon in TestResultRow to draw more attention to the fact that this is a button (I only recently discovered this myself!)

[no-stack-dub-sack]

@iansinnott absolutely, was thinking about this as well. Will add this tomorrow.

[no-stack-dub-sack]

@iansinnott tests are added, let me know if you think this looks good. Thanks!

Also, just added a new commit which addresses some minor typos in the www package.