Switch the 'content' field of notes to allow multiple text parts rather than just a single one.
Update styles for the CodeMirror widget inside the content-list form
Fix i18n key typo
Normalise "empty" things in incoming/outgoing data:

  * Empty strings are dropped (becoming nil)
  * A nil for an array element is replaced with []
Don't allow bibliography or index notes to be subrecords of multipart records.
Musings

Conflicts:

	common/jsonmodel.rb
	migrations/models/marc21.rb
update EAD and MARC exporters to use JSON models

applied logic of previous commit to EAD exporter

Conflicts:

	backend/app/lib/export.rb
	common/jsonmodel.rb
	migrations/lib/exporter.rb
	migrations/models/marc21.rb

update EAD and MARC exporters to use JSON models

Conflicts:

	common/jsonmodel.rb
	migrations/lib/exporter.rb
	migrations/models/marc21.rb
fixed lingering conflict
change all exporters (except EAC) to take json input
Fix 'dates' validation to deal with empty arrays.
Collection management record now complains about not enough elements in its array
Tweak EAD and MARC for the new multipart notes
Merge pull request #310 from hudmol/export-with-json-merged-with-notes

Export with json merged with notes