Add "Package class >> load" and supporting methods
Merge branch 'upstream' into pr-728
Fixed *extension category

Importer-Exporter was renamed to Kernel-ImportExport
added Package >> loadFromNamespace:

... and Package class >> load:fromNamespace:
update API-CHANGES.txt
Merge branch 'upstream' into ext-728

Conflicts:
	API-CHANGES.txt
Merge pull request #765 from herby/ext-728

Fixes #727