fixes https://github.com/TryGhost/Product/issues/3687
After this change, relative URLs in emails will be replaced with
absolute URLs using the post URL. Making relative Portal URLs possible
etc.
Updates the test data generator to fix invalid URL encoding (somehow a
backslash + escaped double quote was added when it wasn't required).
As discussed with the product team we want to enforce kebab-case file names for
all files, with the exception of files which export a single class, in which
case they should be PascalCase and reflect the class which they export.
This will help find classes faster, and should push better naming for them too.
Some files and packages have been excluded from this linting, specifically when
a library or framework depends on the naming of a file for the functionality
e.g. Ember, knex-migrator, adapter-manager
