[UI] Add flags, bytes uploaded/downloaded, RTT to Peers tab on webui

[ppayne]

• add a flags string to each peer indicating the current state of the peer
• add the total bytes uploaded/downloaded by each peer
• add the estimated round-trip time to peers to which we connected

[ppayne]

Actually I created this patch 8 years ago (have had it in my own fork of this repository since 5 August 2016) and have found it invaluable - for some reason I like to know the details about the peers.

I've taken the latest pull from the develop branch, added this code, and tested it locally by building and installing and running.

[ppayne]

I noticed #3499 Stop using deprecated LibTorrent features in which it recommends using torrent.status.flags && lt::torrent_flags::paused.

So I'm wondering if I should try something like peer.flags & lt::peer_flags::interesting rather than peer.flags & peer.interesting (see peer_info).

[ppayne]

Well I've tried every combo I can think of and none work, not lt.peer_flags., not lt.peer_flags_t., not lt::peer_flags::, not lt::peer_flags_t::. The documentation for the Python bindings straight up don't exist.