Move ADMID, refactor createPointerFile

refs #6500

Move ADMID from file element to structMap/div element

Refactor: cleanup and add NSMAP to archivematicaXMLNamesSpaces.  Ensure
elements in pointer file have METS or PREMIS namespace, not unqualified.
Remove unneccessary () from ElementMaker elements.
Add compression event to pointer file

refs #6500

Add compression event and file for the new AIP when compressing AIP,
including tool and version information.  When creating the pointer
file, insert that event and associated agent.
Add link to download pointer files

refs #5716

Add link to download pointer files from Archival Storage tab.  Proxy to
storage service API URL that actually returns the data.  Minor cleanup
in templates to use flexible URLs