first pass at publication object.
Fixed some errors.
Added other properties and fixed erros.
Update document.json

add spike-in concentrations as document type
Update document.json
Merge pull request #327 from ENCODE-DCC/1546-publication-object

1546 publication object
Merge pull request #326 from ENCODE-DCC/1575-Spikeins-type

1575 spikeins type
Merging in master.