Align Hub & Solution "Resource" models

Hub needs to pass in "template" object graphs that are not backed by Solution Items - and this must support uploading of "resources" (images & thumbnails)

The individual templates have an `.assets` array that includes the `name`, `type` and `url`

During item creation, the type-specific module reads assets entries, and the url is used to fetch the resource, and then it is uploaded as a resource of the newly created item.

In my quick read of Solution.js, the individual templates have a `resources` array that is composed of file paths. The paths look like they encode resource folders from the source item, as well as the file name.

I believe if we make the "resource handler" a little "smarter" - i.e. if the entry in the array starts w/ `http` then it should treat it as a full url and not do further processing) then we can align the two systems.

I'll also be putting up a PR to add Solution `schemaVersion` and migration system (#268), which will allow us to perform on-the-fly json translations, which will allow conversion of existing hub-created-solution items into the format supported by Solution.js