Update JS Foundations documentation (Mythical Critters)

[wvmitchell]

Activity to be updated: JS Foundations

Summary of changes needed:

• All of the class based exercises can remain in the repository, however they should be categorized as optional extras demanding independent study, and the Readme should reflect this

Note

The repository for this issue is listed as front-end-curriculum, even though the repository is really turingschool-examples/javascript-foundations. This is due to the fact that the project board cannot belong to more than one org (turingschool vs turingschool-examples)

[hfaerber]

Some mythicals have been revised to make FP. Please do not archive the following suites to the optional extras folder:

• dragon
• vampire
• hobbit