Merge core to avoid warning when check gh-pages

Add HTML version of LAYOUT.md of 317a7c3c

Fix unittest for changes on motivation.md

Telling people to point back to this site

Make templates consistent with how links are checked- v2

Add build of FAQ.html

068cb3ab didn't update the HTML.

Template changes to work with validator according to current link validation rules. Also update HTML output.

Add Unit Test target to Makefile

Explaining the new "deferred" label

Fix error message at validator

Use INFO for http link verification

Test rework

This reverts commit 0b370670.

Revert "Minor changes to make error messages consistent, and possibly less crashy. Still need unit tests to trigger this code."

This reverts commit 8c0819be.

Improve message for glossary error

Minor changes to make error messages consistent, and possibly less crashy. Still need unit tests to trigger this code.

Improve message for glossary error

fill in missing '$ ' in prompt

Improve callout box and "learning objectives" box

Add small script to setup label in lesson repo

Update validator for changes in directory structure