Fix broken links

[wvmitchell]

Description

There are a handful of broken links currently on the FE Curriculum site, these should be updated, or removed.

Task List

• Run the integrity tool to find any links that are currently 404's.
• Update each link to point to an updated resource, or amend the section it appears in to no longer rely on that resource

[letakeane]

@wvmitchell Some of these links aren't actually broken; the Integrity tool just isn't smart enough to recognize them.

For example:

• In the M1 CSS Fundamentals lesson, there's a link to the Web Archive, and it works but just is slow, so integrity times out before it loads.
• In the M2 Intro to the Backend lesson, a link is to localhost:3000, which works when the student has the local server running, but of course would not work for Integrity

Are these okay to leave as is in the curriculum?

[letakeane]

@kaylagordon @Kalikoze @robbiejaeger What are you opinions on this?? See comment above