Proof a few more chapters for flagrant errors.
Proof some more sections for flagrant errors.
App::themePath() is no more.
Fix lies.

Replacing Core classes is more tricky now as namespaces make it much
harder to shadow a class name. However, each section show you how to
load aliased objects. For example loading aliassed helpers.
Merge pull request #1538 from cakephp/3.0-more-proofing

3.0 more proofing