docs: update all links to reflect new refactor

[CaerusKaru]

Almost all of the links in the docs are likely now outdated due to #631

[LauraKirby]

wiki right side nav:

I was able to find the location for one of the broken links.
issue 1: click, "Source Code", should be taken to the source code for the demo application
issue 1 (current behavior): 404
solution: [Source Code](https://github.com/angular/flex-layout/tree/master/src/apps/demo-app)

issue 2: click, "Browser Support", should be taken to information about "Browser Support"
issue 2 (current behavior): "You do not have permission to update this wiki."

issue 3: click, "Adaptive Layouts", then click, "Source", should be taken to the source code for the demo application.
issue 3 (current behavior): 404

What are the steps to reproduce?

• Visit flex-layout wiki
• issue 1: Click on "Source Code"
• issue 2: Click on "Browser Support"
• issue 3: Click, "Adaptive Layouts", then click, "Source"

[CaerusKaru]

@LauraKirby This should be fixed by #664

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