Create a generic attachment picker

We already have the Attachment Selector Macro but it has some issues:

• it was designed to be used for editing an object property that holds an attachment reference (the classname and property parameters are mandatory) so it's not easy to use it as a picker for a macro parameter (e.g. the office viewer macro)
• it's not compact, you always need to open the modal that lists the attachments
• it lists attachments from a single page (either the current page or the one specify by the targetdocname parameter)

We need a generic attachment picker that is similar to the user and page pickers:

• is more compact
• you can filter (suggest input)
• shows attachment icon / thumbnail (as in the Attachments tab)
• visually separate attachments from the current page from attachments from elsewhere (with configuration to show only the attachment from the current/specified page)
• ideally, have a way to upload new attachments

We can then use this picker as:

• custom displayer for a new attachment property XWIKI-15583
• picker for macro parameters (e.g. as HTML displayer for AttachmentReference)