Rename "clarity" to "opacity"

[sambody]

There is a button in the floating panel called "clarity". I would suggest to rename it to "opacity", since that is the term that is used in most drawing software (and in CSS) for that attribute -- sometimes also called alpha, or transparency, which is the opposite of opacity.

Using the same term will make it more clear/intuitive for users who are already familiar with the term. For others, it will not make a difference.

Thanks.