Enum Widget Support

[dihm]

This PR adds basic Enum widget support to BLACS tabs. EnumOutputs are intended to be used for controls that only allow discrete values (ie an Enum-like control). Very basic support for EnumWidgets was added in labscript_utils v3.0.0b1. This PR uses those base widgets to add support for them within a device tab.

Example of EO widgets (from output_classes.py test script)

Incantation within a DeviceTab will look like

eo_prop = {
    'Enum1':{
        'options':['option 1', 'option 2'], # uses default 0-indexing
        'return_index':True, # widget will return integer index instead of string value when queried
    },
    'Enum2':{
        'options':{
            'option 1':{'index':2, 'tooltip':'description 1'},
            'option 2':4, # if tooltip not desired, just pass custom index
        }
    }
}
self.create_enum_outputs(eo_prop)
eo_widgets = self.auto_create_enum_widgets()

self.auto_place_widgets(('Enums', eo_widgets))

I've also updated the test script within device_base_class.py to run and show the new functionality.

It relies on a pre-compiled dummy connection table, which I've placed in a top level tests directory assuming we will eventually get to the point of implementing more rigorous testing.

[Json-To-String]

I can confirm that this works pretty nicely in a few new devices just copying and pasting the snippet for the DeviceTab above, and also that the enum widgets process their updates nicely to the values handled by the Worker. The test works fine too.

What I can't quite replicate is why the docs build seems to have timed out - I can build them locally with seemingly little issue. I'll keep looking into that.