Last Valid Work + usb_cleanup() + dev_width fix + --hotplug/API

API V1.25 - add 'Last Valid Work' time for each device
API - return Last Valid Work
miner.php report 'Last Valid Work' as time before request
Implement and use usb_cleanup() on shutdown or restart
usb_cleanup() use correct locking mechanism
curses - fix - put a dev_width inside #ifdef
Hotplug - allow setting interval via --hotplug or API
api.c fix MSG overlap
README --hotplug
Release MMQ device only once (not 4 times)