Created InterfaceThread class to monitor USB port and cleaned up
Interface Class
Updated initialize window to call currentupdate via signals so that the
reading of current can be toggled on and off.
Changes made in the course of debugging hv bias board interface.
Made the parse current and parse voltage commands safe for string
errors.  Updated the functions to set voltage and get current to check
for errors and retry automatically if they fail.  Sped up the leakage
current read.
Updated Temperature parsing to be safe to all inputs, updated getTemp
routine as to retry twice if it fails.