Working on USBTMC
Working on port part

mdtPortManager inherits no more QThread, but QObject directly.
Removed some ugly msleep() calls from GUI thread.
The new state machine implementation is now done, just some device states could be added in future (DeviceSetup, DeviceError, ...)
There seems that start/stop is now less buggy,  isReady(), isClosed() give a good help in application.
The bad part of this commit is USBTMC: seems to contain many 1000 of bugs, race conditions, etc.. (it's not easy to test with a tolerant instrument like Agilent DSO1000 ..)