Do not run formatters when calling `scribe.setContent`

Now redundant because of mutation observers.
Merge pull request #139 from guardian/oja-tidy-up

Do not run formatters when calling `scribe.setContent`
Create `scribe.registerHtmlFormatter` interface
Rename `HTMLFormatter` to `HTMLFormatterFactory` to reduce confusion
Make `scribe.htmlFormatterFactory` private
Create `scribe.registerPlainTextFormatter` interface
Rename `Formatter` to `FormatterFactory` to reduce confusion
Make `scribe.plainTextFormatterFactory` private
Rename for consistency with DOM API cases
Move events out of constructor and into events plugin
Merge pull request #141 from guardian/oja-tidy-up-3

Tidy up
Merge remote-tracking branch 'origin/master' into oja-tidy-up-4

Conflicts:
	src/scribe.js
Merge branch 'oja-tidy-up-4'
Merge remote-tracking branch 'origin/master' into oja-tidy-up-2
Load `element` API using AMD