Fixes #260: Threshold operationMode of type String

[deinhofer]

• converted operationMode combobox to be of type integer instead of string. In theory string values would be ok, but it seems that the ARE and ACSs are not capable of dealing it
• so maybe think of restricting the value type of a combobox in the bundle_descriptor.

What should be the default value for operationMode? binary?

[klues]

if the default was binary before, it maybe should remain the default, shouldn't it?

[deinhofer]

if the default was binary before, it maybe should remain the default, shouldn't it? Yes, but here the default value was 2 (deadzone) respectively.

But as I could not find any model in bin/ARE/models using the Threshold plugin, it might be irrelevant.

[kingcole]

looks good, thanks for fixing

I'd also go for binary as default a) to avoid problems and b) because it seems the more useful default

[deinhofer]

Ok, so I will merge it.