Remove device.getString(), add value.getTime()

This breaks the console interfaces, but it's the first step towards a
general device manager.
Add timeout argument to getRawValue() methods
First devicemanager code

There's a lot left to be improved and fixed, but it's a (working)
starting
Fix TecpelDMM8061 returning ints instead of floats
Move FunctionDevice functionality to devicemanager

Move the functionality of the FunctionDevice class to a
getCalibratedLastRawValue method in devicemanager.
Remove kivy ui
Update devicemanager
Add getStatus method to devicemanager
Major update

Rewrite ui in qt, some bugfixes and a lot of other stuff
Move .ui files to own directory
Forgot to commit these
Not needed anymore with pyqt ui
Fix getLastRawValue returns None on error

Now returns a NullValue
Add some more documentation
Make GetValuesThread private
Fix console interface