AppDF description should support http:// URLs for binary resources as well as local file names

[oorlov]

If some url schema added to resource filename it might not exist in .appdf archive If there is no url schema filename should be considered as filename in .appdf archive

Needed for application exchange feed (https://github.com/onepf/OpenAEP/blob/master/specification/openaep_spec_1_0.md) to share info about thousands apps without building .appdf archive for each

Behavior for uploader to be discussed