Do not needlessly run formatters when executing `insertHTML` command

The formatters are already run thanks to the `MutationObserver`.
Display output HTML in example

[ci skip]
Merge pull request #132 from guardian/oja-insert-html-tidy-up

Do not needlessly run formatters when executing `insertHTML` command
Add path to sanitizer plugin

[ci skip]
Add failing test normalization formatters
Add failing whitespace test
Tidy up
Add sanitize and prepare phases to HTML formatting
Rename prepare phase to normalize
Do not rely on order of object properties
Document phases