First step to fileData cleanup

- inline the headerSections field
- remove the header object, because neither sorting_order nor bam version is applicable in this format
- remove fileUri for the same reason
Merge remote-tracking branch 'upstream/master' into filedata-move

Conflicts:
	src/main/resources/avro/ga4gh.avdl
Merge pull request #21 from cassiedoll/filedata-move

First step to fileData cleanup