Implemented stub hash_mode settings for core and gtkui

Conflicts:
	deluge/ui/gtkui/addtorrentdialog.py
fix "send buffer watermark too low" warnings

1) Double the buffer only if the performance warning is about that.
2) Change cap to 50MB, since it seems the send buffer watermark should be
roughly your max upload per second.
eg. If your max upload bandwith is 12MB/s(100Mbps),
    the buffer of 13107200(12.5MB) should be OK.
Fix "max outstanding disk writes reached" warnings

Do the same logic as 234a897cf3b1ef5d8eccd21d9aac64c6e83e4625 to max_queued_disk_bytes