Aspect support for cm:content

[marsv024]

Added the concept of proxy types used to create cm:content with aspects containing custom metadata from a type in the data model. These types should never be created directly but only used when uploading data.

When a type is selected as a proxy type in the admin console for uploader plus and a file is uploaded and the proxy type selected in uploaded plus, the uploader will show the form for the type, but the uploaded file will be of type cm:content with all the aspects of the selected type applied.

[douglascrp]

This is a good idea.

[teqnology]

I'm considering making a tiny change, where instead of types or proxy types, we would be able to select standalone aspects directly (that is, aspects not being children of any type/subtype/proxy type. This pull request is definitely the right direction. Just adding a note: currently the model manager doesn't allow to be included in the custom type. So this feature, although very useful, won't work with a content model created through Share. It will only work for the standard xml model bootstrap