[Enhancement] Toggle 'automatic updating' per item
### Feature request / enhancement

Hey! :)

I love that you added "Enable/Disable automatic update" feature it's great!
It would be even better if we could toggle it on and off for each paddy group we create.. because sometimes we need to create buttons or elements which have a minimum size (which is different than the paddings) and we want to resize them manually.

Something similar to how selection in groups work in sketch:
![image](https://user-images.githubusercontent.com/29888529/36966483-994451c0-2065-11e8-8471-5c296e413d4b.png)
We can toggle on or off how selection is made for each particular group instead of a general settings for all groups.

I hope it's something that's possible within sketch's framework!

Thanks,
Zohar
