Updates from Imaging WG Approved decisions at HL7WGM [#3395] ImagingStudy.series.instance 0..*, [#3541] rename dateTime element to start, [#3543] rename accessionNo to accession, [#3544] change imagingStudy.modality to imagingStudy.modalityList, and [#3545] update ImagingStudy top level description. 

git-svn-id: http://gforge.hl7.org/svn/fhir/trunk/build@3221 2f0db536-2c49-4257-a3fa-e771ed206c19