Dvg-devices

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* Minor: Adjusted width of GUI control in ``Julabo_circulator_qdev.py``

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* Loosened dependence to ``pyserial~= 3.4``

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* Added device: Julabo circulator

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* Workaround for bug with unknown cause in ``Aim_TTi_PSU_protocol_RS232`` where
the power supply occasionally will skew the serial input and output stream,
such that the reply matches the second-previous query statement. Fixed by
forcefully flushing the serial input and output buffers whenever a wrong reply
is received. Hopefully, this will fix the skew when the next ``query()``
operation gets executed.

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* Fixed bug in ``BaseDevice.query_ascii()``. The use of ``ast.literal_eval`` got
removed because it chokes on ``nan``. Everything is now interpreted as a
``float`` instead.

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* Fix wrong import statement ``dvg-pyqt-controls``
* Fix wrong import statement ``dvg-pyqt-filelogger``