Attachments: support for direct URL
Description
At the moment it is only possible to get a URL for the Attachment Master of the uploaded attachment. However, there are situations there it is required to be able to obtain a direct URL to download the attached file instead of opening a corresponding master.
Entity Attachment needs to be enhanced with calculated readonly property url: String that would dynamically compute the full attachment's URL (i.e., with the protocol, domain name, etc.). Such URL can be shared with others, embedded as links into RichText documents, etc.
Attachment can represent both files and hyperlinks. The value for url for hyperlink attachments should be the value of the hyperlink.
Include Attachment.url into Attachment Master and Centre.
Expected outcome
Ability to obtains direct URL for file attachments.