Attachments management

RFC: Attachments management

Currently we have only orphaned attachments management implemented.
Meanwhile there's an often case with the boards having hundreds/thousands of attachments which need to be controlled more effectively.
The idea is based on currently implemented feature as a MOD for phpBB 3.0.x named Manage attachments ACP module for phpBB3.
Generally based on orphan attachments management option, it allows to:

• List all files being attached to posts/PMs;
• Split attachments list into pages;
• Display main file information like: real filename, posting time, size, author, download/view count, topic link and name the file belongs to (or PM attachment notice), post's ID the file is attached to;
• Download attachment directly via files list;
• Sort attachments by name/date/size/extension/downloads count/post ID/author name in both directions;
• Filter attachments' list by time displaying entries from previous 1/7/14 day(s) or 1/6/12 month(s).
• Reassign attachments to another posts specifying valid posts' IDs;
• Delete attachments.