Octane guides review: back out of MU project layout for file paths

[mike-north]

In light of Module Unification project layout being de-scoped from the octane edition, we need the updates to the guides (#455) to be converted back to "classic" project layout (/app and /addon folders).

These paths are mostly found in markdown "fenced code blocks"

```hbs {data-filename=src/ui/routes/application/template.hbs}

```

In this case, we'd convert the file path as follows

A top-level template

-src/ui/routes/application/template.hbs
+app/templates/application.hbs

Other examples

A component's JS module

-src/ui/components/hello/component.js
+app/components/hello.js

A component's HBS module

-src/ui/components/hello/template.hbs
+app/templates/components/hello.hbs

A controller

-src/ui/routes/application/controller.js
+app/controllers/application.js

[ghost]

@betocantu has started addressing this in #612. Linking for future contributors.

[dennismende]

With #636 all occurrences of MU project structure file paths should have been changed back to current structure.