base64 attachments
array of files
Only process attachments if an edition allows attachments
Extract attachment text rather than pass in base64 encoded files

Using tika to extract the text from attachements, still need to allow
more types than just PDF.

Otherwise ES stores the encoded file, and there is no way to turn this
off currently using the attachments-mapper plugin.

We might be able to ignore the attachment title, as it's highly likly
to the be first thing in the document
Allow other attachment types to be indexed

Specify while file extentions are indexable from the whitelist
only return the output if the system call was sucessful

There is an edge case if the file has not been virus scanned yet.

Also testing on some files show processing errors, so only add to index
if sucessfull text extraction has occured
Test for attachment data text extraction

Refactor code into attachment data
Move attachment title into the attachments rather than indexable_content

All fields are being searched, so we can move the titles from indexable
content into the attachment data

see rummager:
https://github.com/alphagov/rummager/blob/master/lib/elasticsearch/searc
h_query_builder.rb#L138