add some end 2 end diagnostics and fix dates
Abstract CollectorCursor, and return it from Collector.Run().
Fixup package versions, I think. This stuff is hard.
dotnetrdf literals and @context timeStamps
Enable DateTime UTC round-tripping in CollectorCursor.
More UTC roundtripping.
Add content type to resolver blobs.
Add support for <property> to dependency tree data structure.
Merge branch 'master' into anurse/incrementalcatalogupdate

Conflicts:
	src/Catalog/Collecting/Collector.cs
	src/Catalog/Constants.cs
	src/Catalog/GalleryIntegration/GalleryKeyCollector.cs
	src/Catalog/Maintenance/CatalogContainer.cs
	src/Catalog/Maintenance/PackageCatalogItem.cs
	src/Catalog/context/Container.json
	src/Catalog/context/Resolver.json
	src/Catalog/sparql/ConstructResolverGraph.rq
	tests/CatalogTests/CollectorTests.cs
	tests/CatalogTests/End2EndTests.cs
	tests/CatalogTests/ExportTests.cs