fixes for the TapeDrive project

deviceEpos: check type of the attributes when reconnecting the device (second call to __init__, type in the YAML mapping may be different).

deviceEpos: update the position-related attributes only when the device is connected (the position reading is 0 when disconnected, not generating an error).

device: when SAVE_CHANGE, update also the device config (solve inconsistency in configs after reconnection)

create DeviceNumAttributeBusyWidget, enabled only when the device status is BUSY (when setpoints can be set only if the device is started, e.g. Chiller)

deviceNumAttributeWidget: compare to string "degC" instead of units.degC (pint exception)

deviceDebugWidget: add checkbox for returning commands - fixes #15 (closed) - (avoid crashing hardware not returning anything)

remove deviceOSLibrary which is used only for the Epos and does not much (fixes #18 (closed))