Fixed ExtJS resize frame on Valid Units in Quantity Values

What was the issue? 

When adding "Input Quantity Value" to a class, a resize box starts hovering above the "Valid units" section.

How did you solve it? 

The solution was simple. All I needed for this fix was to change resizable: true into resizable: false

Why is this fix important?

It indeed is important because it's a quality of life fix. 

How does it feel to contribute to a platform such as Pimcore?

The feeling is great because this contribution won't help only me, but also all the other developers working with Pimcore.

And if you want to check out this pull request, just follow the link!