UI improvements
peer: fix uploading
store: nextToDownload readahead depends on pieceLength
store: mv chunk.piece generation to piece
store: catch onValidCbs exceptions
socket: console.warn instead of error
store: CHUNK_LENGTH = 16 KB

broke transmission & µTorrent
peer: try to make requests more agile
peer: check sock
peer: cancel in all other peers upon reception

may slow it down?
Revert "peer: cancel in all other peers upon reception"

This reverts commit 398e984ec1e50f788c9c91524eaac88fc50270d6.
app: min refresh interval 300ms
main.html: peer state titles
TODOs