[$40] - Update TopcoderHeader and Challenge Listing to properly support links within the app

[birdofpreyru]

At the moment, all links in the standard TopcoderHeader component lead to the main Topcoder website, thus they use <a>, which, if a link address is changed to an endpoint within Community App, reloads the app when clicked. These links should be updated to use <Link> from utils/router to seamlessly support both remote or local URLs.

The same applies to the links to the Challenge Detail pages from Challenge Listings.

[Colinh84]

Can you assign me to this issue please?

[birdofpreyru]

@Colinh84 Consider yourself assigned. I have just noticed that I don't have enough rights in the repo to add contributors, and without it, I cannot technically assign people who are not contributors. Once my rights corrected, I'll fix it.