metadata-strict for 1.5

[mvahowe]

I think this is the same as or similar to a proposal by @ericpyle a week or so ago. The plan would be to retrofit 2.1 checking of 1.5 values that are required in order to produce valid 2.1. Not having this in the 1.5 schema means that PT users don't discover the problem with their metadata until they try to upload and, in addition, the server errors are not very helpful.

My concern when something like this was first mentioned was that I don't think we can change the 1.5 schema under people. But we could produce a schema with a different name so that PT can use it.

This will not be a huge amount of fun to do since the 1.5 schemas are somewhat arcane to unpick, but, that aside, it ought to be largely a question of copying and pasting from 2.1.

[ericpyle]

@mvahowe another thing to tighten is the country iso code, which the old metadata format allowed either two or three letters, now accepts only two. So metadata-strict needs to be changed to only allow two letters for country code