Add a new text note type to multipart notes
Move the 'content' property from the abstract note into the schemas that use it
Updated factory definitions to reflect the fact that multipart notes don't have content properties anymore.
Frontend changes to show errors when multipart notes are missing a text subnote.
Only skip custom validations if we've already logged a failure for a given property.

Previously all custom validations would be skipped if any validation had
failed, but this prevented more than one custom validation from being reported
at a time.  For example, two notes might be missing subnotes of type text, but
only one would be reported.
Factories fixes
Rework date validation to use Ruby's inbuilt date parsing rather than regexps.
Have EAD import create text subnotes as required.  Updated the tests to match.
Update MARC import to use the new note_text subnote for content
Update Digital Objects & EAC importers for the new note_text subnotes
Update exporters to pull note content out of text note subnotes too.
Modify RDE to work with the new multipart text subnotes
Update JSONModel tests for note changes
Update Resource spawning to use the new notes format
Update Selenium test to match new multipart note format
Clean and format note content for subnotes too
Replace 'Show Advanced' text link with an arrow
Only render the left border on results lists when rendering the components tree
Update aspace_form_helper.rb

Space fix
Merge pull request #524 from hudmol/interleaved-notes-merged

The many changes for multipart notes with a text subnote (instead of a content property)