PREMIS schematron is expecting PREMIS 2 and so won't validate PREMIS 3

[ross-spencer]

Archivematica points users at the web interface for this tool so that users can validate their METS output before storing AIPs. Having recently updated to include PREMIS 3 in the output, we are now seeing this error:

I have traced it to the best of my abilities to this assert in the schematron:

pim/public/schema/pim.stron

Lines 18 to 26 in 1795bc9

	<rule context="mets:mets">
	<assert test="count(//mets:xmlData/pre:object) +
	count(//mets:xmlData/pre:agent) +
	count(//mets:xmlData/pre:rights) +
	count(//mets:xmlData/pre:event) > 0 or
	count(//mets:xmlData/pre:premis) = 1" see="bp-1a bp-1b">
	There must be PREMIS elements inside the METS container.
	</assert>
	</rule>

And I can get past this error if I modify the namespace to expect PREMIS 3 but then I start to see additional assertion errors, so a more expert view on how the schematron could be modified would be appreciated. For example, understanding the basis for other assertions such as PREMIS bitstream and file objects must be contained in a METS techMD

Happy to submit a PR if it helps. This is an incredibly useful tool.

Cheers,