Update asset creation for attachments

### Update Asset Creation JSON API for Attachments ###

I don't think the current asset creation api really works for attachments.  There is a files parameter in which to upload files, but there is no way to associate the meta-data (uuid, product, source level, etc.) with these attachments.  This data is need to determine if the operation being requested is a create or update since the create and update methods are the same.  Additionally as multiple ids can be created as a result of a file upload.  But, the return type of createOrUpdate is a single id.  Also, with the current http invoker interface there is a way to pass a reference to a file on a shared filesystem, in this way the file does not need to be included in the http request.  Losing this ability may present some performance issues.  So:

1. I have changed the files parameter in createOrUpdate to attachments, this takes an array of attachment objects (defined in attachment.schema pulled from the interchange)
1. I have changed the return type of createOfUpdate to be an array of ids, instead of an single id
1. I have added a file property in the attachment schema that can be used instead of the bytes property to specify a path to a file on the local filesystem.  We will need to pay attention to the security implications of this in the implementation (possibly by ignoring the file attribute when authenticated by apiToken)
1. Add attachment uuids to the asset delete method, for deleting specific attachments.