- moved logic into a Missing singleton
- shouldn't try to download duplicates anymore, only requests a hash
once every 5 minutes and not from the same host
- removed obsoleted variables
- the "Objects to be synced" in the Network tab should now be correct
- removed some checks which aren't necessary anymore in my opinion
- fix missing self in Throttle (thanks landscape.io)
- send buffer to send multiple commands in one TCP packet
- recv/send operation size now based on bandwith limit
- send queue limited to 100 entries
- buffer getdata commands to fill send queue, instead of waiting for the
data packet to arrive first (i.e. allow getdata to work asynchronously)
